Analysis of the Aroma Composition of Different Varieties of Apricot Wine

Abstract

Fruit wine is favoured by consumers because of its low alcohol content and unique taste, but there are few studies on apricot wine. In order to explore the quality of apricot wine obtained by fermentation of different varieties of apricots and the typical volatile substances in apricot wine, and to find apricot varieties that can brew better quality apricot wine, the gas chromatography-mass spectrometry (GC-MS) method was used to detect Jinkaite, Katy, Jintaiyang apricots and brewed apricot wine, and the correlation and difference of key odour substances were analyzed. A total of 25 aroma components in 6 categories were detected in the 3 varieties of apricots. Among the components, esters account for the largest proportion at 14 types, followed by both ketones and alcohols at 5 types. Compared with the original juice, the types of volatile substances in fermented apricot wine increased significantly. After aroma component analysis, 42, 36 and 38 odour components were screened out in Jinkaite wine, Kate wine and Jintaiyang wine. They were mainly composed of alcohols and esters. Among the three varieties, the total content of aroma components in “Katy” wine was the highest (114.09 mg·L⁻¹), followed by Jinkaite wine (112.17 mg·L⁻¹), and the total content of aroma components in Jintaiyang wine was lower (108.72 mg·L⁻¹). The following substances were the most important aromatically active compounds identified, and they had low olfactory thresholds: linalool (25 μg·L⁻¹), β-ionone (0.007 μg·L⁻¹), ethyl caprylate (12.87 μg·L⁻¹), methyl caprate (6 μg·L⁻¹), which has a larger OAV value and strongly influences the aroma characteristics. Multi-factor analysis showed that compared with other varieties of apricot wine, the highest score of Kinkate apricot wine is 89 points, which is golden yellow, showing rich floral and fruity aromas, soft and full body, good stability and strong typicality. Jinkaite apricot, as an early-maturing and excellent new variety selected from the natural hybrid seedlings of Katy apricot, can be used as a high-quality new wine-making raw material. The aroma components and content of apricot wine made from different varieties of apricots showed significant differences, which provided an important basis for the selection of raw materials for deep processing of apricots. The research and development of apricot wine products can not only solve the problem of deep processing of apricots, but also conform to the current development trend of the wine market and have a good market prospect.

1. Introduction

Apricot (Prunus armeniaca L.) is native to China and belongs to Rosaceae, subfamily Prunoideae, genus Prunus [1]. Apricot is tasty, brightly coloured, rich in trace elements and essential vitamins [2], and widely recognised by consumers due to its pleasant flavour and rich nutrition [3]. The strong aroma of apricot fruits enhances the market popularity of the fruit and is one of the most important indicators of high commercial value at maturity. Different varieties of apricots contain different flavour components [4]. Aromatic fruits are more attractive and more competitive in the market under the condition that the quality requirements of apricots in the domestic and foreign markets are constantly improving [5].

Katy apricots are nearly round and the fruit is large, with an average fruit weight of 105 g and a maximum of 135 g. The semi-ripe peel is orange-yellow, the top of the fruit is flat, the suture line is medium-deep, the halves are asymmetrical, and the peduncle is medium-deep. The peel is medium thick, not easy to peel off, the flesh is orange-yellow after full ripeness, hard solute, fine flesh, more juice, soluble solids content of 13.6%, sweet and sour flavour, aroma, and quality. The pits are small and detached. It is resistant to storage and transportation, and can be stored for about 7 days at room temperature. The yield of 3-year-old trees was 18.8 kg, which is good [6].

Jinkaite apricot is an early-maturing and excellent new variety selected from the natural hybrid live variety of Katy apricot. Previously, Xue Xiaomin, the corresponding author of this work, published an article about the Jinkaite apricot, exploring the advantages of Jinkaite apricot, the specific content is as follows: Jinkaite apricot fruit surface is golden yellow, smooth and beautiful, and there is a red glow on the sunny side when it is fully ripe. The flesh is orange, the juice is abundant, the flesh is delicate and crisp, the soluble solid content is 14.0%, the aroma is rich, the flavour is sweet and sour, and the quality is excellent. The kernel is medium and large, separated from the pit, and the edible rate is 96.2%. The skin is thick and tough. The fruit is resistant to storage and transportation, and can be stored for 10 days at room temperature. The fruit was extra-large and oval, with an average single fruit weight of 119.0 g and a maximum fruit weight of 158.0 g. The yield was high, with an average plant yield of 10.2 kg in the fourth year, equivalent to 45,288.0 kg·hm⁻² per mu [7].

Jintaiyang apricot is a new variety of medium-ripe sweet apricot. The fruit is nearly round and spherical, the flesh is delicate, the taste is sweet, the average single fruit weight is 67.1 g, and the maximum fruit weight can reach 88 g. The fruit surface is yellow, and the sunny side has a red hue, the flesh is yellow, the core is separated, the fruit is not cracked, and the fruit contains a variety of amino acids and trace elements. It is rich in nutrition, with an edible rate of 96.8%, delicate meat, lesfibreer, more juice and aroma, soluble solid content of 14.5%, and sweet flavour. It can be stored for about 10 days at room temperature, with high hardness and storage and transportation [8]. The three apricot varieties show significant differences in aroma composition and content, and these differences provide an important basis for the creation of apricot-characteristic aroma varieties and the selection of raw materials for deep processing such as apricot juice, fruit vinegar and fruit wine.

Fruit wine is a variety of beverage wines made from fruit raw materials through fermentation, pressing, clarification, filtration and ageing. As a distinction, wine is primarily produced from fermented grapes, whereas fruit wines are derived from the fermentation of non-grape fruits. Fruit juices are rich in fermentable sugars, and moderate amounts of acids [9], as well as strong aromas and bright colours, giving fruit wines a unique quality and style. Apricot fruit is rich in a variety of vitamins, minerals, polysaccharides, organic acids, dietary fibre and trace elements, etc. Due to the various advantages of apricot, apricot wine also contains a variety of compounds, which are beneficial to human health. Apricot fruit wine development is a very important part of the apricot processing industry. Processing apricots into fruit wine boosts their economic value and reduces waste. It also solves the short shelf-life issue of apricots, promoting apricot deep processing and increasing the variety of fruit wines [10].

Aroma is one of the important factors determining the sensory quality of apricot wine, which is affected by apricot variety, fermentation process, yeast, gelatin, storage and other factors [11]. In recent years, there have been few foreign studies on apricot wine, while domestic research on apricot wine has mainly focused on the optimization of the fermentation process and the screening of yeast. There are few studies on the effect of apricot varieties on the flavour of apricot wine. Pu Xilei et al. brewed wine with Xinjiang small white apricots and performed aroma analysis, and found that apricot wine was fermented to produce a large amount of 3-methyl-1-butanol, isoamyl acetate, ethyl caprylate, ethyl decanoate, ethyl benzoate, linalool, and eugenol, which conferred strong banana, lemon, pineapple, and citrus flavours to the apricot wine [12]. Xu Jia et al. found a total of 28 volatiles in Katy’s apricot wine, mainly including alcohols, esters, aldehydes, acids and alkanes, which are five types of flavour substances. Among them, 10 alcohols, 9 esters, 3 acids, 2 alkanes, 1 aldehyde and 3 others [13].

In addition to the alcohols, esters, acids, aldecorones and ketones commonly found in fruit wine, monoterpene alcohols such as linalool, terpineol, nerolil alcohol, and ionophilol are unique to apricot fruit wine, indicating that the aroma components contained in apricot fruit wine will be different due to different apricot varieties. In order to make full use of apricot resources and find apricot varieties that can produce better quality apricot wine, the aroma composition analysis of apricot wine made from three kinds of apricots provides a more comprehensive and accurate understanding of the various aroma components contained in apricot wine, and provides a reliable theoretical basis for the study of wine making characteristics of different apricot varieties. The research and development of apricot wine products can not only solve the problem of deep processing of apricots, but also conform to the current development trend of the wine market and have a good market prospect.

2. Materials and Methods

2.1. Materials and Reagents

2.1.1. Materials

The test samples were Jinkaite, Katy and Jintaiyang apricots, provided by the Shandong Institute of Pomology. The experimental site had uniform terrain conditions, sandy loam soil, flat terrain, and good growth and fruiting. The fruits were all harvested at full ripeness, with Jinkaite apricot harvested 70 days after full bloom (1 June 2023), Katy apricot harvested 75 days after full bloom (7 June 2023), and Jintaiyang apricot harvested 68 days after full bloom (4 June 2023) for standardized harvesting. Select the fruits with suitable maturity, no pests and diseases, and no mechanical damage from the periphery of the tree canopy for random fruit picking. After harvesting, they were immediately transported to the laboratory under normal temperature (25 ± 2 °C) conditions, with transportation time controlled within 4 h, and subsequent experimental treatments were conducted within 2 h of arrival.

2.1.2. Chemical Reagents

Pectinase (food grade): Shanghai Yuanye Biotechnology Co., Ltd., Shanghai, China; white sugar (grade 1): Taikoo Co., Ltd., Hong Kong, China; 2-octanol, sodium chloride (all analytically pure): Sinopharm Chemical Reagent Co., Ltd., Shanghai, China; Saccharomyces cerevisiae EC1118: Lallemand Brewing Co., Ltd., Montreal, QC, Canada.

2.1.3. Instruments and Equipment

GC-MS QP2020 gas chromatography-mass spectrometry: Shimadzu Corporation, Kyoto, Japan; Eyela water bath: Shanghai Ailang Instrument Co., Ltd., Shanghai, China; SPX biochemical incubator: Beijing Yong Guangming Medical Instrument Co., Ltd., Beijing, China.

2.2. Methods

2.2.1. Brewing Method

Brewing Process of Apricot Wine

Fresh apricot fruits were selected and washed, kernels and stalks were removed, and then they were crushed in a juicer, filtered and placed in a fermentation bucket. The soluble solids content of Jinkaite apricot, Katy apricot and Jintaiyang apricot pulp were 10.6 °Bx, 10.9 °Bx and 11.2 °Bx, respectively, and about 120 g of white sugar (The main ingredient is sucrose) were added to supplement the carbon source to make the soluble solid content to 19 °Bx. After even mixture, pectinase was added at 0.1 g·L⁻¹, and a water bath was applied at 45 °C for 2 h. After one day’s standing, inoculation of brewer’s yeast EC1118 was carried out. The inoculation rate of yeast was 2 g·L⁻¹, 6 g of active dry yeast was weighed in 20 mL of 50 g·L⁻¹ sugar water, placed in a 35 °C water bath for 30 min, and then the activated yeast was cooled to room temperature before inoculation. Then fermentation was carried out at a constant temperature of 17 °C.

2.2.2. Analysis and Detection

Determination of Volatile Flavour Substances:

The detection of aroma substances in the three raw juices and apricot wines was carried out by headspace solid-phase microextraction combined with gas chromatography-mass spectrometry (HS-SPME-GCMS; Perkin Elmer Co., Ltd., Waltham, MA, USA) for qualitative and quantitative analysis.

(1) Pre-treatment conditions for SPME: when 8 mL of the three kinds of apricot juice and apricot wine were taken into a 20 mL headspace vial, 2 g of NaCl was added, and 20 μL of sec-octanol at a concentration of 0.1 g·L⁻¹ was added as the internal standard, and the extraction head (DVB/C-WR/PDMS, 80 μm, 10 mm; Perkin Elmer Co., Ltd., Waltham, MA, USA) would be ageing for 5 min at 200 °C in an AOC-6000 autosampler (Perkin Elmer Co., Ltd., Waltham, MA, USA), which was preheated and stirred for 10 min at 50 °C. The sample was then inserted into the extraction fibre and adsorbed at 50 °C for 20 min, and the extraction head was thermally desorbed at 230 °C for 5 min in the inlet of GC.

(2) GC-MS Analysis Conditions: split injection, and keep the carrier gas (helium) at a constant flow rate of 1.5 mL/min; the column was InertCap-WAX (30 m × 0.25 mm × 0.25 μm; Perkin Elmer Co., Ltd., Waltham, MA, USA), and the column heating procedure was 40 °C to keep for 5 min, 2 °C/min to 130 °C, then 5 °C/min to 220 °C for 10 min, total running time 60 min. The inlet temperature was 230 °C, and the ion source temperature was 230 °C, and the electron ionization source was in the 70 eV mass spectrometry scanning range of m/z from 35 to 350.

Qualitative and Quantitative Determination of Aroma Components: qualitative method: the qualification of aroma compounds was carried out using standard retention time comparison, retention index comparison and NIST 2017 mass spectral library query. Quantitative analysis: the quantification of each aroma component was carried out using the internal standard method, which was calculated by equation:

$$\mathrm{C}\mathrm{i}=\mathrm{C}\mathrm{s}\times (\mathrm{A}\mathrm{i}/\mathrm{A}\mathrm{s})$$

where: Ci is the content of an aroma component, μg·L⁻¹; Ai is the peak area of an aroma component; Cs is the content of 2-octanol (internal standard), μg·L⁻¹; As is the peak area of 2-octanol (internal standard).

Evaluation of aroma components: Odour activity value (OAV) is a method that can objectively and comprehensively evaluate the contribution of an aroma component to the overall aroma of apricot in terms of the content of the aroma component and the aroma threshold [14]. The OAV value is used to evaluate the contribution of each aroma component to the overall flavour of apricot, and the aroma component with OAV > 1 is considered to contribute to the overall flavour of apricot, and the larger the OAV value is, the greater the contribution is. The OAV value (OAVi) of each aroma component can be calculated by the following formula:

$$\mathrm{O}\mathrm{A}\mathrm{V}\mathrm{i}=\mathrm{P}\mathrm{i}/\mathrm{T}\mathrm{i}$$

where: Pi is the content of volatile flavour substances, μg·L⁻¹; Ti is the aroma threshold value of an aroma component, μg·L⁻¹.

2.3. Data Processing and Statistical Analysis

All indicators were subjected to 3 repetitive tests and the experimental data were analysed and processed using SPSS 25.0. And presented the results as mean ± standard deviation. Significance analysis was conducted, with p < 0.05 indicating significant differences and p < 0.01 indicating extremely significant differences. PCA plots were created using the Novo Magic platform. Graphs were made using Graphpad Prism 10.

3. Results

3.1. Physical and Chemical Indicators

3.1.1. Brix Changes During Fermentation

Sugar level has an important effect on the quality of apricot wines such as taste, flavour, colour and stability. The three apricot wines successfully completed fermentation, and the change in sugar level during fermentation is shown in Figure 1. The highest fermentation rate reached in 1–5 d, with the most drastic change in brix, the fermentation rate decreased slightly in 6–9 d, and the sugars that could be utilized by the yeast gradually decreased as the fermentation progressed, and the fermentation eventually leveled off, and stabilized at 5 °Bx on the 11th day, with no further changes, and the alcoholic fermentation basically ended. The alcohol content of Jinkaite wine, Katy wine, and Jintaiyang wine is 9.03%, 8.55%, and 9.55%, respectively.

3.1.2. Other Fermentation Parameters in the Fermentation Process

The pH values of Jinkaite wine, Katy wine, and Jintaiyang wine were 3.5, 3.4 and 3.7, respectively. The dissolved oxygen content was determined by the dissolved oxygen analyzer method, and the probe sensor end of the dissolved oxygen analyzer was slowly immersed in the apricot wine about 20 cm, and the dissolved oxygen values were 3.48 μg·L⁻¹, 3.59 μg·L⁻¹, and 3.52 μg·L⁻¹, respectively.

3.2. Aroma Analysis of Three Kinds of Apricot Fruits

The aroma compositions detected in different fruits were quite different. As shown in Figure 2. A total of 17 components were detected in Jinkaite, and the content was higher at 26.23 mg·L⁻¹, including 11 esters, 3 alcohols, 1 acid, 1 ketone and 1 hydrocarbon. In Katy, a total of 11 ingredients were detected with a lower content of 4.10 mg·L⁻¹, of which 7 were esters, 2 were alcohols, and 2 were ketones. A total of 14 components were detected in Jintaiyang at 5.03 mg·L⁻¹, of which 7 were esters, 5 were alcohols and 3 were ketones.

The experimental results of this study showed that the main constituents of Jinkaite apricot were esters, alcohols, and aldehydes, which was the same as the results of Xue [15] et al. Yin Yanlei [16] et al. also found a low content of aroma components in Katy apricot. In addition, Wang Jiaxi [17] et al. concluded that the main aroma components of Jintaiyang apricot were alcohols, aldehydes, ketones, esters and acids, and the results of this experiment were the same.

The main aroma components of the fruits of the three apricot varieties are esters, alcohols and ketones. For the same compounds, the relative contents of different varieties of apricots vary greatly. Among them, the ester content of Jinkaite is the highest (17.96 mg·L⁻¹), accounting for 67.18% of the total content, Jintaiyang is (1.54 mg·L⁻¹), accounting for 30.64% of the total content, and Jintaiyang has the lowest content (1.41 mg·L⁻¹), accounting for 34.43% of the total content. The alcohol content of Jinkaite is the highest (7.37 mg·L⁻¹), accounting for 27.56% of the total content, Jintaiyang is (1.82 mg·L⁻¹), accounting for 36.20% of the total content, and Katy has the lowest content (0.53 mg·L⁻¹), accounting for 1.30% of the total content. The ketone content in Katy was the highest (2.62 mg·L⁻¹), accounting for 64.27% of the total content, and that in Jintaiyang was (1.67 mg·L⁻¹), accounting for 33.16% of the total content. The content in Jinkaite was the lowest (1.14 mg·L⁻¹), accounting for 4.25% of the total content. The content of olefins in Jinkaite was the highest (0.14 mg·L⁻¹), accounting for 0.51% of the total content, and was not detected in Katy and Jintaiyang. The content of acids in JinKaite was the highest (0.13 mg·L⁻¹), accounting for 0.49% of the total content, and was not detected in Katy and Jintaiyang.

The fruit of Jinkaite apricot contains relatively high contents of methyl acetate and ethyl acetate among the ester substances, relatively high contents of 2,3-butanediol among the alcohol substances, and relatively high contents of 2-octanone among the ketone substances. The fruit of Katy apricot contains relatively high contents of methyl acetate and isoamyl acetate among the ester substances, relatively high contents of 2,3-butanediol among the alcohol substances, and relatively high contents of 2,3-butanedione and 1-methoxy-2-propanone among the ketone substances. The fruit of Jintaiyang apricot contains relatively high contents of γ-dodecalactone and ethyl acetate among the ester substances, relatively high contents of linalool and dihydro-β-ionol among the alcohol substances, and relatively high contents of 1-methoxy-2-propanone and β-ionone among the ketone substances.

Mohamed A. Farag et al. [18] used gas chromatography-mass spectrometry (GC-MS) to determine the aroma components of ripe apricot fruits of various varieties in Egypt and believed that alcohols and esters represented the main categories of apricot volatiles. Linalool, anethole, dihydro-β-ionone, β-ionone, γ-decanoate, dihydro-actinolide, γ-laurolactone and methyl palmitate were the characteristic aroma components of apricot. Gokbulut et al. believe that ethanol, hexanal, hexyl acetate, 1-hexanol, etc., are present in most apricot varieties [19].

3.3. Analysis of Aroma Components of Three Types of Apricot Wine

Make a PCA plot according to the data in

Table 1. Three aroma substances of apricot wine.

Variety	Aroma Substances	Aroma Description	Threshold·L−1	Jinkaite	Katy	Jintaiyang	p-Value
				Aroma Component Content	Aroma Component Content	Aroma Component Content
acid	3-Methylbutylarachidate			-	265.47 ± 12.28	-
	Hexanoic acid	Fat, cheese	420	29.18 ± 5.23 c	75.75 ± 1.86 b	94.93 ± 5.37 a	<0.001
	benzoic acid	Chemical	1000	30.72 ± 2.86 a	35.14 ± 6.24 a	31.64 ± 8.42 a	0.678
Olefins	Megastigma-4,6(E),8(Z)-triene			360.65 ± 1.05	-	-
	β-Myrcene	Fruity; Grape; Wine		37.35 ± 4.47	-	126.58 ± 5.09
	D-Limonene	lemon; orange; citrus		32.29 ± 8.25	-	-
alcohol	Isobutanol	Fusel	40,000	326.18 ± 9.76 a	286.63 ± 7.27 b	318.84 ± 2.52 a	<0.001
	Isoamyl alcohol	Fusel	30,000	26,718.2 ± 3.65	27,668.24 ± 8.66	28,219.13 ± 4.72	<0.001
	Linalool	Citrus scent Floral sweet rose scent Woody	25	282.51 ± 6.71	-	1313.35 ± 3.87
	Phenylethyl alcohol	Fresh bread aroma, sweet rose-like fragrance	1000	693.88 ± 8.33 c	864.78 ± 10.24 a	731.11 ± 3.64 b	<0.001
	Dihydrogen-β-Ionol	1-Methoxy-2-Propanol Plastic Smell	30,908	132.93 ± 6.12	-	201.77 ± 8.04
	L-.α.-Terpineol	lilac	120	-	-	403.95 ± 5.38
	Citronellol	Floral scent	40	-	-	98.12 ± 6.48
	trans-Nerolidol	lemon		-	39.24 ± 4.27	28.74 ± 0.95
	Farnesol			-	41.85 ± 3.91	-
ester	Hexyl formate			710.59 ± 5.53	316.84 ± 6.1	-
	Ethyl benzoate	Cherry, grape, ylang-ylang aroma, bitter and astringent	53	282.82 ± 7.83	-	-
	Methyl acetate			-	1439.39 ± 2.48	1677.21 ± 5.73
	Ethyl acetate	Sweet fruit aroma, ethereal aroma, wine-like taste	880	3702.53 ± 2.14 b	1790.27 ± 7.3 c	4592.77 ± 8.02 a	<0.001
	Hexyl acetate	Pear, cherry, banana and other sweet fruity aromas	1500	132.73 ± 6.79	-	-
	Ethyl propionate		1800	71.02 ± 4.18	-	-
	Isoamyl acetate	Banana, pear	30	572.96 ± 3.38 b	596.68 ± 3.4 a	189.87 ± 3.41 c	<0.001
	Ethyl butyrate	Banana, pineapple	20	33.57 ± 5.62 c	79.37 ± 2.58 a	61.59 ± 1.12 b	<0.001
	Ethyl hexanoate	Green Apple	55.33	724.55 ± 6.53 a	665.93 ± 8.85 b	580.85 ± 3.51 c	<0.001
	Methyl octanoate	Sweet, aldehyde smell	0	175.8 ± 2.1 a	167.17 ± 0.28 b	163.25 ± 4.98 b	0.016
	Ethyl Caprylate	Creamy, waxy, fruity like apricot, sweet wine, pineapple	12.87	9618.53 ± 8.7 b	11,391.88 ± 7.2 a	9102.46 ± 8.23 c
	Propyl Caprylate			59.27 ± 3.47 a	41.87 ± 6.37 b	68.23 ± 3.95 a	<0.001
	Isoamyl Caprylate			762.83 ± 5.43 b	779.08 ± 10.72 a	594.2 ± 1.68 c	<0.001
	Ethyl nonanoate			130.48 ± 1.47 b	151.51 ± 5.34 a	158.22 ± 7.85 a	0.002
	Methyl decanoate		6	1031.11 ± 6.85 c	2861.35 ± 4.8 a	2034.69 ± 7.83 b	<0.001
	Ethyl decanoate	Fruity, winey, fatty	1122.3	41,203.92 ± 12.68 b	46,611.59 ± 4.08 a	39,556.96 ± 2.03 c	<0.001
	Propyl decanoate			209.79 ± 4.55 a	194.68 ± 9.56 b	204.52 ± 4.35 ab	0.077
	Isobutyl Decanoate			111.77 ± 9.38 ab	121.76 ± 11.77 a	96.47 ± 0.75 b	0.084
	Ethyl benzoate			-	-	221.51 ± 8.97
	4-Methylpentyl-8-Methyl nonanoate			53.17 ± 5.59	-	-
	Isobutyl laurate			-	78.36 ± 4.39	-
	Isoamyl laurate			296.74 ± 7.46 c	534.1 ± 8.07 a	359.36 ± 1.61 b	<0.001
	9-Methyl hexadecenoate			65.37 ± 3.96 b	51.85 ± 3.84 c	118.67 ± 2.69 a	<0.001
	E-11-Ethyl hexadecenoate			200.77 ± 3.79	-	178.16 ± 10.31
	9-Ethyl hexadecenoate			1870.63 ± 7.97 c	2276.39 ± 8.64 b	3695.65 ± 5.4 a	<0.001
	Ethyl oleate			1921.15 ± 6.1 c	3023.47 ± 10.99 a	2540.73 ± 9.19 b	<0.001
	10-Trans,12-Cis-octadecadienoic acid methyl ester			330.35 ± 2.39	-	-
	Trans-9,12-Octadecadienoic acid propyl ester			7341.37 ± 5.36 b	7959.57 ± 6.07 a	6120.79 ± 125.08 c	<0.001
	γ-Decanolide	Caramel, wax, fruity, creamy, peach and coconut aroma		93.87 ± 5.64 c	759.85 ± 3.44 a	336.87 ± 1.96 b	<0.001
	Dihydroactin			69.37 ± 4.88	-	-
	Methyl linolenate			1017.08 ± 5.19 b	827.27 ± 4.71 c	1174.75 ± 7.24 a	<0.001
	(Z)-Ethyl cinnamate			-	42.53 ± 8.46	-
	γ-Dodecalactone	Fruity, sweet, nutty	0	-	-	222.62 ± 12.56
	Methyl stearate			63.29 ± 5.12 a	33.39 ± 5.45 b	54.47 ± 3.85 a	<0.001
ketone	β-Ionone		0.2	184.6 ± 7.78 a	45.87 ± 3.92 b	33.59 ± 5.57 c	<0.001
	Farnesyl acetone			92 ± 6.41	271.27 ± 7.13	-
	acetone			3575.94 ± 1.32 a	1742.42 ± 2.87 b	1455.69 ± 6.2 c	<0.001

Note: Different letters indicate significant differences (p < 0.05), “-” indicates not detected.

, as shown in Figure 3, and the data are correct. The levels of substances detected are listed in Table 1. As shown in Table 1, the aroma components detected in apricot wine brewed from different varieties of fruits are quite different. A total of 42 components were detected in Jinkaite wine, with a content of 112.17 mg·L⁻¹, including 29 esters, 5 alcohols, 3 ketones, 3 hydrocarbons, and 2 acids. A total of 36 components were detected in Katy wine, with a higher content of 114.09 mg·L⁻¹, including 25 esters, 5 alcohols, 3 acids, and 3 ketones. A total of 38 components were detected in Jintaiyang wine, with a lower content of 108.72 mg·L⁻¹, including 25 esters, 8 alcohols, 2 ketones, 2 acids, and 1 hydrocarbon.

The main aroma components of the three apricot wines are alcohols and esters. For the same compounds, the relative contents of different varieties of apricot wines are distinct Among them, the ester content is the highest in Katy wine (82.77 mg·L⁻¹) and the lowest in Jintaiyang wine (75.7 mg·L⁻¹); the alcohol content is the highest in Jintaiyang wine (31.28 mg·L⁻¹) and the lowest in Jinkaite wine (28.15 mg·L⁻¹); the ketone content was the highest in Jinkaite wine (3.85 mg·L⁻¹) and the lowest in Jintaiyang wine (1.49 mg·L⁻¹); the content of olefins in Jinkaite wine was (0.42 mg·L⁻¹) and was not detected in Katy wine; the acid content was the highest in Katy wine (0.37 mg·L⁻¹) and the lowest in Jinkaite wine (0.06 mg·L⁻¹).

3.3.1. Esters in Apricot Wine

Ester compounds have long been considered contributors to the perception of fresh and pleasant odours, with aroma characteristics such as floral and fruity aromas [20]. Volatile ester compounds largely determine the fruity aroma associated with wine and other fermented beverages [21]. As shown in Table 1, among the five types of compounds in apricot wine, ester compounds have the highest content. According to the aroma threshold of different substances, the contribution of each substance to the aroma of apricot wine varies, but the threshold of ester compounds is generally low and easy to taste, so they play an important role in the flavour of apricot wine and the quality of the wine. In total, 29, 25 and 25 ester substances were detected in the three apricot wine samples, respectively. Among them, the ester content in the Katy wine sample was higher (82.77 mg·L⁻¹), the ester content in the Jinkaite wine sample was (79.69 mg·L⁻¹), and the ester content in the Jintaiyang sample was the lowest (75.7 mg·L⁻¹).

A total of 34 esters were detected in the wine samples, including 4 acetates, 12 ethanol esters and 18 other esters, of which ethanol esters were the most numerous. Ethanol esters, also known as fatty acid ethyl esters, mainly medium-chain fatty acid ethyl esters (MCFAEEs) include ethyl butyrate (fruity), ethyl caproate (banana), ethyl caprylate (pineapple), ethyl caprate (fruity and floral) and ethyl laurate, which are described as providing fruity and floral aromas to wine [21]. Fatty acid ethyl esters are one of the most important volatile compounds in wine, and most of them have the typical fruity aroma of wine. This group of esters makes a positive contribution to the overall quality of wine [22]. Its content and type also have an important impact on the quality of apricot wine.

The ethanol ester content in the apricot wine samples is ranked in order of size: Katy wine>Jinkaite wine>Jintaiyang wine. The ethanol esters with higher content in the three wine samples include ethyl caprate (fruity, winey aroma), ethyl caprylate (waxy, orange fruity, rosey aroma), ethyl elaidate, 9-16-carbon ethyl acetate, ethyl acetate (sweet fruit aroma, ether aroma, wine-like taste), hexyl acetate (sweet fruit aroma such as pears, cherries, bananas, etc.). Compared with the apricot juice before fermentation, the ethyl acetate content in Jinkaite apricot wine and Jintaiyang apricot wine was 3.55 and 9.81 times higher than that in apricot fruit, respectively. The content of ethyl caprate in Jinkaite wine was significantly increased, which was 100.7 times that of apricot fruit. Isoamyl laurate was not detected in apricot fruit, but the content in apricot wine was 0.95 mg·L⁻¹. The content of isoamyl acetate in Kinkate apricot wine and Kate apricot wine was 2.57 times and 5.78 times that of apricot fruits, respectively.

3.3.2. Alcohol Compounds in Apricot Wine

Alcohols are the second largest aroma substance in apricot wine, with the aroma of rose, lilac and lily of the valley. It is mainly formed by yeast metabolism and hydrolysis of glycosides and esters [23]. Higher alcohols have a strong pungent odour and have a significant impact on the sensory properties of wine and other fruit wines and brandies [24,25]. Studies have shown that an appropriate mass concentration of higher alcohols (<300 mg·L⁻¹) can increase the complexity of the aroma of wine, while a higher mass concentration (>400 mg·L⁻¹) will give the wine a chemical taste. Destroy the sensory quality of wine [26].

Five, five and eight alcohols were detected in the three apricot wine samples, respectively. The highest alcohol content was found in the sample of Jintaiyang wine (31.28 mg·L⁻¹), the lowest in the Katy wine sample (28.9 mg·L⁻¹), and the lowest in the wine sample of Jinkaite (28.15 mg·L⁻¹).

Eight alcohols were detected in apricot wine, namely isobutanol, isopentanol, linalool, phenylethyl alcohol, dihydro-β-ionol, L-alpha-terpineol, citronellol, trans-nerolidol, and farnesol. Isobutanol, isopentanol, and phenylethyl alcohol were detected in all three wine samples. The first two substances can give the wine a vegetable or peppery fusel aroma [27]. Isopentanol has a pungent and spicy odour characteristic, which is related to the odour of herbal plants. When the concentration is lower than 300 mg·L⁻¹, it is beneficial to increase the complexity of the wine [28]. Phenylethyl alcohol is mainly formed by yeast metabolism and is a key odourant that causes honey and rose aromas [29].

Linalool is considered to be the main aroma contributor in “Xiao Ye Zhu Gan” apricot [30]. Linalool and dihydro-β-ionol were detected in the wine samples of Jin Kate and Jin Tai Yang. L-alpha-pinpineol was only detected in the wine sample of Jintaiyang.

3.3.3. Main Aroma Components in Apricot Wine

The ratio of the content to the olfactory threshold is calculated to obtain the odour active value (OAV). It is generally believed that only substances whose content exceeds their olfactory threshold can be perceived by humans, that is, only substances with an OAV greater than 1 contribute to the aroma of wine.

The OAVs greater than 100 are ethyl caprylate, methyl caprate and β-ionone. These three substances contribute greatly to the aroma of apricot wine. The first two can bring fruity and creamy aromas such as pineapple to the wine. β-ionone has a lower threshold, resulting in a high aroma activity value, and has strong raspberry and violet aromas, as well as fruity and woody aromas. It brings a significant floral aroma to the overall scent of Jinkaite wine. Violet ketone was not detected in Katy and Jintaiyang Apricot wine, which may be the reason for their lack of floral aroma. The OAVs greater than 10 are ethyl caproate, ethyl caprate and linalool. The first two have fruity, floral and fatty aromas, while linalool has lilac and rose aromas. The OAVs between 1 and 10 are ethyl acetate and hexyl acetate. Ethyl acetate has a sweet fruity aroma, and hexyl acetate can give the wine a sweet and fruity aroma such as pear, cherry and banana. Isobutanol and isoamyl alcohol were detected in the apricot wine of Kinkate, Kate and Golden Sun, and the contents of isobutanol (326.18 μg·L⁻¹, 286.63 μg·L⁻¹, 318.84 μg·L⁻¹), isoamyl alcohol (26,718.2 μg·L⁻¹, 27,668.24 μg·L⁻¹, 28,219.13 μg·L⁻¹). Although they bring fusel taste, due to the high aroma threshold, isobutanol 40,000 μg·L⁻¹ and isoamyl alcohol 30,000 μg·L⁻¹ had no significant contribution to the aroma of apricot wine, and did not show any bad odour.

3.3.4. Effects of Different Varieties of Apricots on Apricot Wine During Fermentation

In apricot wine, in addition to the common alcohols and esters produced during fermentation, it also contains terpenes such as linalool, pinene, and violet alcohol, which are characteristic aromatic compounds derived from apricots [31]. Terpenes are secondary metabolites synthesized from acetyl-CoA in plants [32], and due to their elegant aroma and low olfactory threshold, they significantly contribute to the fragrance of fruit wines [33]. There are certain differences in the aroma components of apricot wine brewed from different varieties of apricots, indicating that different varieties of apricots can bring different aroma characteristics to apricot wine.

Methyl acetate is the main aroma component of Jinkaite apricot, in addition to the higher content of aroma components such as ethyl acetate, methyl caprylate, isoamyl acetate, β-ionone, linalool, etc. Jinkaite wine has the largest variety of flavour substances, including ethyl benzoate (cherry, grape, ylang-ylang aroma), hexyl acetate (pear, cherry, banana and other sweet fruity aromas), ethyl caprate (fruity, winey, fatty aroma), β-ionone (violet floral aroma), linalool (citrus, floral, sweet rose aroma) and so on. Compared with apricot fruits, the content of ethyl caprate in Jinkaite wine was significantly increased, which was 100.7 times that of apricot fruit, 3.55 times that of ethyl acetate, and 2.57 times that of isoamyl acetate in apricot fruit. Among them, β-ionone and linalool are the characteristic aroma compounds brought by Jinkaite apricot fruit. Jinkaite apricot wine has a fruity aroma, harmonious aroma, and typical apricot flavour.

The main aroma component of Katy apricot is 1-methoxy-2-acetone (mint), in addition to methyl acetate, 2,3-butanediol, and methyl palmitate. Katy has the highest total content of aroma components and the highest ester content. Including ethyl caprate (fruity, winey, fatty aroma), ethyl acetate (sweet fruit aroma), ethyl 9-hexadecenoic acid, etc. The content of isoamyl acetate in Katy apricot wine is 5.78 times that of apricot fruit. It also contains isoamyl alcohol, farnesylacetone, etc. The fruit wine is rich in flavour.

1-Methoxy-2-acetone is the main aroma component of Jintaiyang Apricot, and the key aroma components are γ-decanolactone, linalool, γ-dodecanolide, ethyl tridecanoate, and the aroma components with higher content are dihydro-β-ionol, 2,3-butanediol, methyl palmitate. Jintaiyang Wine contains more alcohols, including linalool (citrus, floral, sweet rose smell), phenethyl alcohol (fresh bread aroma, sweet rose-like floral aroma), dihydro-β-ionol, L-.alpha.terpineol. The contents of dihydro-β-ionol and linalool in Jintaiyang apricot wine were 2.59 and 6.58 times that of apricot fruits, respectively. And also contains γ-dodecanolactone (fruity, nutty), ethyl caprylate (creamy, fruity apricot, sweet wine, pineapple) and so on. The ethyl acetate content in Jintaiyang apricot wine was 9.81 times that of apricot fruit.

3.3.5. Sensory Evaluation

Formation of the Tasting Team

Refer to the method adjustment evaluation criteria in the national standard QB/T5476-2020 “General Technical Requirements for Fruit Wine” [34]. The sensory tasting scoring and evaluation criteria are shown in

Table 2. OAV values of aroma compounds.

Category	Aroma Substances	Threshold μg·L−1	OAV Value
			Jinkaite	Katy	Jintaiyang
alcohol	Isobutanol	40,000	0.01	0.01	0.01
	Isoamyl alcohol	30,000	0.89	0.92	0.94
	Linalool	25	11.37	-	52.53
	Phenylethyl alcohol	1000	0.69	0.88	0.73
	Dihydro-β-Ionol	30,908	0.00	0.00	0.01
	L-alpha-Terpineol	120	-	-	3.38
ester	Ethyl benzoate	53	5.36	-	-
	Ethyl acetate	880	1.48	2.03	5.22
	Hexyl acetate	1500	0.08	-	-
	Ethyl propionate	1800	0.04	-	-
	Ethyl hexanoate	55.33	13.07	11.85	10.56
	Ethyl Caprylate	12.87	747.49	885.06	837.02
	Methyl decanoate	6	172.11	477.55	337.68
	Ethyl decanoate	1122.3	36.70	41.53	-
ketone	β-Ionone	0.007	950.50	-	-

Note: “-” indicates not detected.

,

Table 3. Sensory evaluation criteria.

Indicator	Scoring Criteria	Score/Points
Colour (15)	The wine has a golden yellow colour with a slight red hue, clear and free of sediment.	12–15
	The wine is darker in colour and slightly cloudy	8–11
	The wine is dark yellow, cloudy and opaque	<8
Aroma (20)	The aroma is complex, pure and pleasant, with apricot fruit characteristics	15–20
	The aroma is pure, with fruit aroma and no bad smell	10–14
	There is a miscellaneous smell and a distinctly bad odour	<10
Taste (40)	The wine is soft, fresh, well-balanced and well-balanced	35–40
	The wine is harmonious, refreshing and clean	30–34
	It has miscellaneous flavours and a bland body	20–29
	The wine is rough-bodied, slightly pungent, and poorly balanced	<20
Flavour (15)	It has the characteristic flavour of apricot wine and the ester aroma is obvious	12–15
	The flavour profile is not obvious, and there is an ester aroma	8–11
	It has no characteristic flavour of apricot wine and is defective	<8
Overall Impression (10)	good	7–10
	average	<7

and Table 4. The judging panel consisted of 11 members, including 5 males and 6 females. The members are composed of professional professors and students from Qilu University of Technology between the ages of 20~40 and related majors, and the finished apricot wine produced by the brewing test is evaluated from five aspects: body colour, aroma, taste, flavour and overall feeling. The evaluators need to go through 3 times a week, 1.5 h each time, a total of 30 h of theoretical knowledge and evaluation practical training, sensory training, for a period of about 2 months, and the assessment and training are carried out in the professional sensory evaluation laboratory. The training content mainly includes sensory evaluation methods and mastery of basic theoretical knowledge of apricot wine, wine-tasting operation training and scale-use training.

Sensory Tasting of Wine Samples

At room temperature of 25 °C, the tasting team leader poured the apricot wine samples into a 50 mL transparent tasting glass labelled with a three-digit random code, with a sample volume of about 30 mL. Immediately presented in a random order, the evaluators independently sniff and taste the samples to be tested without external interference, and each of them obtains their own tasting results. After each sample evaluation, rinse the mouth with purified water, and the rest interval between each sample is 5 min, to eliminate the effect of carryover from the previous sample on the next sample, and to avoid olfactory fatigue, and the experiment is repeated three times.

Sensory Evaluation Results

The sensory evaluation of apricot wine made from different varieties of apricot showed that the wine sample with Jinkaite wine had the highest sensory score of 86.9 points, followed by the wine samples made with Katy wine, with a sensory score of 83.8 points, while the wine samples fermented with Jintaiyang apricot had a lower sensory score of 80.9 points (Table 4). From the perspective of appearance, the wine samples of Jinkaite wine and Katy wine were light yellow in colour, crystal clear and pleasing to the eye, with good clarity, while the wine samples of Jintaiyang wine were darker in colour, orange, with average clarity and gloss, so the appearance score was lower. From the perspective of taste, the wine samples of Jintaiyang wine and Katy wine had higher acidity, light body and refreshing taste, while the acidity of Jinkaite wine was lower. Apricot wines brewed with different processes can meet the needs of different consumers, and can also be used as base wines for blending to make the taste of apricot wine more balanced.

Table 4. Sensory scores of apricot wines.

	Colour (15)	Arom (20)	Taste (40)	Flavour (15)	Overall Impression (10)	Score (100)
Jinkaite	11.13 ± 0.4 ab	18.39 ± 0.7 a	35.94 ± 2.08	13.58 ± 0.82 a	8.63 ± 0.3 a	86.91 ± 1.55 a
Katy	12.29 ± 1.36 a	16.58 ± 0.68 b	37.26 ± 1.36	11.18 ± 1.1 b	7.11 ± 1.05 b	83.76 ± 2.08 ab
Jintaiyang	10.12 ± 0.45 b	17.41 ± 0.5 ab	34.78 ± 2.02	12.07 ± 0.9 ab	8.03 ± 0.5 ab	80.91 ± 2.19 b

Note: Different letters indicate significant differences (p < 0.05).

Table 4. Sensory scores of apricot wines.

	Colour (15)	Arom (20)	Taste (40)	Flavour (15)	Overall Impression (10)	Score (100)
Jinkaite	11.13 ± 0.4 ab	18.39 ± 0.7 a	35.94 ± 2.08	13.58 ± 0.82 a	8.63 ± 0.3 a	86.91 ± 1.55 a
Katy	12.29 ± 1.36 a	16.58 ± 0.68 b	37.26 ± 1.36	11.18 ± 1.1 b	7.11 ± 1.05 b	83.76 ± 2.08 ab
Jintaiyang	10.12 ± 0.45 b	17.41 ± 0.5 ab	34.78 ± 2.02	12.07 ± 0.9 ab	8.03 ± 0.5 ab	80.91 ± 2.19 b

Note: Different letters indicate significant differences (p < 0.05).

4. Discussion

In the unique aroma of apricot fruit, the role of a specific flavour component should be very limited, which can be missing and replaced, and the typical apricot aroma is manifested through the interaction between components such as fusion, superposition, and masking [33]. Compared with apricot fruits, the types of volatile compounds in apricot wine increased significantly after fermentation. The aroma components of apricot wine can also be caused by the interaction of different substances.

A total of 42 components were detected in Jinkaite wine, and the content was 112.17 mg·L⁻¹, including 29 esters, 5 alcohols, 3 ketones, 3 hydrocarbons, and 2 acids. Higher levels included ethyl benzoate (0.28 mg·L⁻¹, cherry, grape, ylang-ylang aroma), hexyl acetate (0.13 mg·L⁻¹, sweet and fruity aroma of pear, cherry, banana, etc.), ethyl caprate (41.2 mg·L⁻¹, fruity, winey, faty), β-ionone (0.18 mg·L⁻¹ violet floral), linalool (0.28 mg·L⁻¹ citrus, floral, sweet rose scent) and so on. Brings a rich fruity and floral aroma to the Jinkaite apricot wine. A total of 36 components were detected in Katy’s wine, and the content was 114.09 mg·L⁻¹, including 25 esters, 5 alcohols, 3 acids and 3 ketones. Katy has the highest total content of aroma components and the highest ester content. Including ethyl caprate (46.61 mg·L⁻¹ fruity, winey, fatty aroma), ethyl acetate (1.79 mg·L⁻¹ sweet fruit aroma), ethyl 9-hexadecenoic acid (2.28 mg·L⁻¹), etc. A total of 38 components were detected in Jintaiyang Wine, and the content was as low as 108.72 mg·L⁻¹, including 25 esters, 8 alcohols, 2 ketones, 2 acids and 1 hydrocarbon. Jintaiyang Wine contains more alcohols, including linalool (citrus, floral, sweet rose smell), phenethyl alcohol (fresh bread aroma, sweet rose-like floral aroma), dihydro-β-ionol, L-.alpha.terpineol, and also contains γ-dodecanolactone (fruity, nutty), ethyl caprylate (creamy, fruity apricot, sweet wine, pineapple) and so on.

The three types of apricot wine have fruity aromas such as apricot, grape, cherry, banana, peach, apple, pear and floral aromas such as locust flower and ylang-ylang. Among them, the apricot fruit aroma in the JinKaite wine sample is obvious, the Katy wine sample contains peach, coconut and other fruity aromas, and the Jintaiyang wine sample contains obvious citrus and floral aromas. All three samples contained yeasty flavours such as bread and biscuits, which may have been caused by the wine samples coming into contact with the lees during storage. In general, Katy is mainly fruity and fresh, while Katy and Jintaiyang have more complex aromas and obvious floral aromas.

The aroma components detected in apricot wine made from different varieties of fruit were quite different.

Fu Li to Saimaiti apricot wine, small white apricot wine, Beishan apricot wine, Qiaoer fat apricot wine, round dan apricot wine, tree dry apricot wine. A total of 70 aroma compounds were detected in 6 kinds of apricot wine, including 27 alcohols, 19 esters, 11 acids, and 12 other 12 species. In addition to the alcohols, esters, acids, and aldehydes and ketones commonly found in fruit wine, apricot wine also contains monoterpene alcohols such as linalool, terpineol, nerolil alcohol, and ionophilol, which are unique components of apricot wine. The results of this study are consistent with this [35].

A total of 93 volatile compounds were detected in Xiangbai apricot wine, with a total content of 1555.13 μg/L. Among them, the volatile compounds with higher content were alcohols, esters and acids, accounting for 47.9%, 41.0% and 7.0% of the total volatile compounds content of apricot liquor, respectively. The apricot liquor fermented with apricot juice retained 57 original aroma components, and the content of 60% volatile compounds was significantly increased, and 38 new volatile compounds were added after fermentation [36].

Liu Tingting fermented and produced plum fruit wine from whole fruit and pomace, respectively, and the main aroma components of the two kinds of fermented wine were ethyl octanoate. Among the two fruit wines, the compounds with relatively high aroma activity and outstanding aroma were ethyl caprylate, β-damone ketone, linalool, ethyl caproate, and phenethyl alcohol. The whole-fruit fermented wine has an aroma similar to that of almonds, with both fat and fruity aromas. Pomace fermented fruit wine has a distinct fruity aroma, with both floral and sweet aromas, and the aroma is long-lasting and stable [37].

5. Conclusions

The main aroma components of the apricot wine were analyzed by GC-MS technology, and 25 aroma components in 6 categories were detected in the three varieties of apricots, and esters accounted for the largest proportion of each component, followed by ketones and alcohols. A total of 42, 36 and 38 odour components were detected in Jinkaite, Katy and Jintaiyang, respectively. It is mainly composed of alcohols and esters. Among the three varieties, Katy had the highest total content of aroma components, followed by Jinkaite, and Jintaiyang had the lowest total content of aroma components. Linalool, β-ionone, ethyl caprylate, methyl caprate, ethyl acetate, ethyl caproate, etc. were the most important aromatic active compounds identified, and the OAV value was large, which strongly affected the aroma characteristics, and were the basic aroma components and typical aroma substances of apricot wine. The sensory tasting score of Jinkaite Apricot Wine is 89 points, slightly higher than the other two apricot wines. Jinkaite apricot wine has a fruity aroma, soft taste and light yellow colour, which has the typical characteristics of apricots, indicating that Jinkaite apricots are more suitable for the development of fruit wine.

This study made some progress in exploring the chemical characteristics of apricot wine, but we are also aware that there are certain limitations in this study, such as the limited sample size. We will conduct fermentation experiments with more varieties of apricots in follow-up research to find varieties that are more suitable for winemaking.