Evaluation of Lipid and Protein Oxidative Stability of Meat from Growing Rabbits Fed Avocado Waste

Abstract

The objective was to evaluate the effect of the inclusion of avocado waste (AW) in the diet of rabbits on lipid composition, color, and lipid and protein oxidative stability in the meat of growing rabbits. For this purpose, 80 male rabbits (New Zealand × California) with an average initial weight of 945 ± 47 g were fed for 28 days, being randomly distributed to one of the four experimental treatments (T) (T1: 0%, T2: 4.32%, T3: 8.39%, and T4: 12.25% of waste avocado inclusion, respectively). A decrease (p < 0.05) in the amount of saturated fatty acids was observed in the meat of rabbits fed 8.39% and 12.25% AW, a lower (p < 0.05) concentration of malondialdehyde (mg MDA/kg) in the meat of rabbits fed the AW, and a lower (p < 0.05) concentration of dinitrophenylhydrazine (DNPH) in the treatments with 4.32 and 8.39% AW. The results suggest that the addition of AW in rabbit diets increases the content of n-3 polyunsaturated fatty acids and protects the meat from the products of lipid and protein oxidation, decreasing discoloration and delaying oxidation, generating a final product with a longer shelf life.

1. Introduction

Rabbit meat is an alternative for producing excellent quality animal protein due to its nutritional properties, high content of unsaturated fatty acids (UFAs), and low content of saturated fatty acids (SFAs) and cholesterol [1]. The sensory quality of meat perceived by consumers is of great importance for preference selection, with meat color being the main attribute associated with freshness and wholesomeness. The content of lipids present in meat influences the sensory aspects of meat. Lipid and protein oxidation limit quality and acceptability, because they are responsible for biological modifications causing a negative effect on meat color [2]; this occurs through water loss, production of toxic compounds, alterations in color, rancidity, and putrefaction, generating anomalous aromas in meat [3]. Oxidation products generated during refrigerated storage are an important cause of meat quality deterioration and a reduction in consumer acceptance of the product. Rabbit meat is a white meat [1], and it is potentially vulnerable to the detrimental effects of oxidation on cardiovascularly healthy meat. This an important issue as demand for rabbit meat products is increasing [4]. In addition, it contains high levels of UFA, which is desirable for a cardiovascularly healthy meat [5]; however, this implies a higher risk of oxidation of polyunsaturated fatty acids during a prolonged period of storage [6]. For this reason, it is of great interest to modify the fatty acid profile of rabbit meat and increase the shelf life of the meat. Dietary modification when feeding rabbits is a viable method for adding value to rabbit meat to provide benefits to the consumer [7].

The use of agro-industrial wastes that are discarded due to their size or physical damage is considered to be of great importance; regarding their nutritional composition, they are an alternative that can be used in animal feed [8]. Avocado (Persea americana Mill.) is a rich source of energy, since it has a large amount of vegetable fat, in which mainly UFA or sterols of biological interest prevail due to the presence of phenolic compounds and pigments with antioxidant activity [9]. The addition of avocado in animal feed has only been documented in a few scientific articles, where they evaluate the effect of including it in the diet on the nitrogen and energy balance in pigs [8], the modification of the composition of pig muscles [10], and in vitro digestibility and in situ degradability in sheep [11].

It is considered that the nutritive value of waste avocado offered in a complete form (pulp, peel, and seed) in rabbit feed could increase the shelf life of meat by retarding the oxidation process due to the phenolic compounds present in the avocado peel and seed. The present study was conducted to evaluate the effect of the inclusion of waste avocado paste on the oxidative stability and meat quality of growth-finishing rabbits.

2. Materials and Methods

This research project (4536/2018/CI) was approved by the Bioethics and Animal Welfare Committee of the Facultad de Medicina Veterinaria y Zootecnia of the Universidad Autónoma del Estado de México.

2.1. Rabbits and Housing

Eighty male rabbits of the New Zealand x California breed with an average initial live weight of 945 ± 47 g were randomly divided into four groups assigned to one of the four diets (0%, 4.32%, 8.39%, and 12.25% waste avocado inclusion, respectively) for 28 days (

Table 1. Composition and chemical analysis of experimental diets.

Ingredients	Avocado Waste (% as Feed)
	0	4.32	8.39	12.25
Soybean meal	0.00	4.89	4.75	4.62
Canola meal	20.82	11.91	11.19	10.32
Wheat bran	22.55	21.87	21.24	20.67
Sorghum	22.96	21.76	20.18	22.46
Alfalfa hay	4.87	6.61	6.42	6.25
Oats hay	27.14	27.03	26.26	21.90
Premix 1	0.76	0.74	0.72	0.70
CaCO3 2	0.90	0.87	0.85	0.83
Total	100.00	100.00	100.00	100.00
Chemical composition
DM 3 (%)	82.71	85.42	84.93	80.12
DE 4 (MJ/kg DM)	10.75	11.79	12.80	13.97
CP 5 (%)	16.25	16.61	16.29	16.52
EE 6 (%)	1.39	1.47	1.57	2.23
CF 7 (%)	14.00	15.00	15.83	15.49
Ash	6.61	6.44	6.36	6.51
Ca 8 (%)	0.80	0.79	0.79	0.78
P 9 (%)	0.64	0.59	0.59	0.60
Total of fatty acids (%)
SFA 10	18.8	21.74	25.27	25.82
MUFA 11	37.65	37.67	39.84	40.27
PUFA 12	43.56	40.59	34.9	33.91

¹ Premix: Saccharomyces cereviciae 50 g, mynasel 100 g, compactor 300 g, antibiótic 60 g, coccidiostat 33 g, calcium carbonate 1100 g, betaine 100 g, phytase 10 g, calcium 14.28%, phosphorus 0.026%, ash 46.34%. ² Calcium carbonate, ³ dry matter, ⁴ digestible energy, ⁵ crude protein, ⁶ ether extract, ⁷ crude fiber, ⁸ calcium, ⁹ phosphorus, ¹⁰ SFA: saturated fatty acid, ¹¹ MUFA: monounsaturated fatty acid, ¹² PUFA: polyunsaturated fatty acid.

), in individual cages (40 cm × 60 cm) of galvanized steel with their respective feeder and drinker. At the end of the experiment, 40 rabbits (10 rabbits per treatment) were used to evaluate the lipid profile and 40 rabbits (10 rabbits per treatment) to evaluate the oxidative stability of the meat.

2.2. Ingredient and Experimental Diets

The avocado paste (Persea americana Mill.) was elaborated using Hass variety wastes, the fruit was collected from a packing company in the municipality of Xalisco, State of Nayarit, and the avocados were ground in fresh form with a mobile hammer mill without a sieve to obtain a homogeneous mixture of the complete avocado (pulp, seed, and peel). The avocado waste (AW) was stored at room temperature in plastic containers for later use. The chemical nutritional analysis of AW is presented in

Table 2. Chemical composition of avocado waste paste.

Nutrient	Content
Dry matter, %	30.17
Crude protein, %	5.50
Ether extract, %	46.95
Ash, %	3.27
Crude fiber, %	17.94
Total energy, Kcal/Kg	6203
Saturated fatty acid (%)	32.26
Monounsaturated fatty acid (%)	51.9
Polyunsaturated fatty acid (%)	15.6

. In the control treatment (T1) no avocado waste was added; in treatments T2, T3, and T4, 4.32%, 8.39%, and 12.25% (wet basis) of AW were included, respectively. The diets were pelleted and formulated to meet the growth-finishing requirements established by the NRC [12] and Lebas [13] (Table 1).

2.3. Sample Collection

At the end of the experimental period, the rabbits were slaughtered according to the Mexican Official Norm procedure [14] with an average live weight of 2036 ± 119 g. Immediately after slaughter, the rabbits were eviscerated according to the procedure described by Blasco and Ouhayoun [15] and the carcass was kept refrigerated at 4 °C for 24 h. Subsequently, the Longissimus dorsi muscle was removed from the 40 carcasses destined to evaluate lipid and oxidative stability and fatty acid analysis. The use of the Longissimus dorsi muscle was due to the accessibility and size of this muscle; furthermore, this is an indicator of meat quality, oxidative stability, and the fatty acid profile. This makes it a standard model in research related to meat quality.

Burgers of 66 g were made with rabbit meat; for each treatment of each sample, three replicates were obtained, differentiated from day 0, 4, and 8 of refrigeration, respectively. In the preparation of the rabbit burgers, a ring was used as a conventional mold with an oval shape of 10 cm in diameter and 1 cm thick. The burgers corresponding to day zero were kept frozen at −20 °C, wrapped in aluminum foil. These samples were not thawed prior to the measurements, as the objective was to halt any oxidative processes and preserve the sample in its frozen state for subsequent oxidation tests. Similarly, the burgers corresponding to days 4 and 8, once their refrigeration period at 4 °C had elapsed (under permanent fluorescent light for 24 h a day to simulate the sales conditions of traditional marketers), were also frozen at −20 °C for the same purpose of halting oxidative processes and preserving them for later analysis. The frozen meat from all samples (day 0, 4, and 8) was directly used for these analyses.

2.4. Total Fatty Acid Profile

Fatty acid content in meat was determined by gas chromatography according to the method described by Rodriguez-Maya et al. [16]. A total of 1 μL of each sample was injected into the gas chromatograph (Perkin Elmer, Clarus 500 model); fatty acids (FAME: Fatty acid methyl ester acronym) were separated in a capillary column with 100 m × 0.25 mm inner diameter × 0.2 μm film thickness (SUPELCO TM-2560); the separation was obtained with a temperature ramp (140 °C for 5 min with increments of 4 °C per min up to 240 °C), using nitrogen as a carrier gas. Retention times were compared with commercial standards (SUPELCO37, FAME MIX analytical SIGMA USA).

2.5. Color Measurement

Surface color measurements of rabbit meat model systems at day 0, 4, and 8 of chilling were performed using a Minolta Chromameter CR-400 colorimeter (Minolta Camera Corp., Meter Division, Ramsey, NJ, USA). The chroma colorimeter consisted of a 10 mm diameter head measuring area and a data processor. Color measurement was performed using the CIELAB scale as recommended by the international meat commission; L*, a*, b*, C*, and H° values were recorded to obtain brightness, redness, yellowness, chroma, and hue values, respectively.

2.6. Substance Reactive to Thiobarbituric Acid (TBARS)

The TBARS analysis was performed under the methodology described by Ganhão, Estévez, and Morcuende [17] with modifications from Hernández et al. [10]. A total of 5.0 g of burger was homogenized in falcon tubes by adding 15 mL of 3.8% perchloric acid and 0.5 mL of 4.2% butylated hydroxytoluene (BHT) in ethanol. During homogenization, the plastic tubes were kept immersed in ice to minimize the production of new oxidative reactions during the extraction of thiobarbituric acid-reactive substance (TBARS). After homogenization, the tubes were centrifuged at 3000 rpm for 4 min at 4 °C. An aliquot of 2 mL was mixed with 2 mL of TBA (0.02 M) in a glass tube with a screw cap. The tubes with the sample and the standard curve were placed in boiling water at 100 °C for 45 min. After this time the glass tubes were allowed to cool, and the absorbance of the resulting mixture was measured at 532 nm. The standard curve was prepared using 1,1,3,3-tetraethoxypropane (TEP) at a concentration of 0.2282 g TEP/L. Lipid oxidation of the samples was measured at 0, 4, and 8 days of refrigeration storage.

2.7. Quantification of the Carbonyl Group of Proteins

Protein oxidation, measured by total carbonyl content, was assessed by derivatization with dinitrophenylhydrazine (DNPH) according to the procedure described by Ganhão, Morcuende, and Estévez [18] with modifications by Hernández et al. [10]. Protein concentration was calculated from absorption at 280 nm. The number of carbonyls was expressed as nanomole of carbonyl per milligram of protein using an absorption coefficient of 21 nM⁻¹ cm⁻¹ at 370 nm for proteins. The same samples were used for TBARS measurement.

2.8. Statistical Analyses

Data were analyzed with PROC MIXED with the AR(1) covariance structure. Fixed effects were considered for the treatments and random effects for the samples of rabbit meat within the measurement periods. Data of the fatty acid profile was analyzed by analysis of variance (ANOVA) with a completely randomized experimental design, using the general linear model (GLM) procedure with the aid of the SAS (2012) [19] statistical program. Comparison of means was performed using Tukey’s test adjusted to consider significant differences between means if p < 0.05 [20]. For variables with repeated measures, color, substance reactivity to thiobarbituric acid (TBARS), and quantification of the carbonyl group of proteins were analyzed with PROC MIXED.

3. Results

3.1. Total Fatty Acid Profile

The total fatty acid profile of the Longissimus dorsi muscle of rabbits fed diets supplemented with waste avocado paste is shown in

Table 3. Total fatty acid profile of Longissimus dorsi muscle of rabbits fed diets supplemented with waste avocado paste.

Item	Avocado Waste (% as Feed)				SEM 1	p-Value
	0.00	4.32	8.39	12.25
SFA 2	41.89 a	42.10 a	41.40 a	40.49 b	0.436	0.043
MUFA 3	34.02 b	35.58 ab	36.68 ab	37.23 a	0.710	0.020
PUFA 4	22.49	20.83	20.56	20.49	0.862	0.333
PUFA n-3 5	0.73 b	0.90 ab	1.05 a	1.11 a	0.078	0.009
PUFA n-6 6	21.98	20.18	19.81	19.70	0.849	0.227

¹ SEM: standard error of the mean, ² SFA: saturated fatty acid, ³ MUFA: monounsaturated fatty acid, ⁴ PUFA: polyunsaturated fatty acid, ⁵ PUFA n-3: polyunsaturated fatty acid series n-3, ⁶ PUFA n-6: polyunsaturated fatty acid series n-6, ^a,b Means in the same row with different superscripts are significantly different (p < 0.05).

. There were differences (p < 0.05) between treatments in total saturated fatty acids (SFAs) and monounsaturated fatty acids (MUFAs), with meat from rabbits fed 12.25% AW having the lowest SFA content, contrary to treatments with 0%, 4.32%, and 8.39% AW which were statistically equal.

A higher (p < 0.05) amount of SFA was observed in the meat of rabbits fed with the 0.0% AW diet compared to the other treatments. A higher (p < 0.05) amount of MUFA was observed in the meat of rabbits fed with the 12.25% AW diet compared to the other treatments. Higher (p < 0.05) total n-3 series polyunsaturated fatty acid (n-3 PUFA) content was observed in the meat of rabbits who were fed 8.39% and 12.25% AW compared to the 4.32% AW diet, with the control diet showing the lowest n-3 PUFA content in meat.

3.2. Color Measurements

Table 4. Meat color of rabbits fed diets supplemented with waste avocado paste during days 0, 4, and 8 of maturation.

Item	Avocado Waste (% as Feed)				SEM 1	p-Value
	0.00	4.32	8.39	12.25
Luminosity L*
Day 0	50.43 ab,x	50.79 ab,x	50.19 b,x	51.77 a,x	0.426	0.055
Day 4	48.59 y	48.93 xy	47.81 y	49.75 y	0.610	0.174
Day 8	48.54 y	48.65 y	47.64 y	48.84 y	0.937	0.817
Redness a*
Day 0	16.94 x	16.30 x	16.56 x	15.72 x	0.343	0.074
Day 4	14.38 x	15.20 x	15.84 x	14.63 x	0.617	0.331
Day 8	11.47 z	11.57 y	13.16 y	11.15 y	0.900	0.431
Yellowness b*
Day 0	9.31 a,y	9.16 ab,y	8.92 ab,y	8.74 b,y	0.154	0.042
Day 4	10.16 x	10.49 x	10.22 x	10.28 x	0.169	0.539
Day 8	10.27 x	10.55 x	10.05 x	10.15 x	0.285	0.640
Chrome C*
Day 0	19.35 a,x	18.7 b,x	18.83 ab,x	17.99 b,x	0.346	0.046
Day 4	17.66 y	18.52 x	18.88 x	17.89 x	0.539	0.340
Day 8	15.47 z	15.85 y	16.59 y	15.09 y	0.609	0.402
Hue H°
Day 0	28.53 z	29.35 z	28.41 z	29.12 z	0.510	0.493
Day 4	35.47 y	35.08 y	33.04 y	34.87 y	1.097	0.402
Day 8	42.12 x	42.96 x	37.58 x	42.32 x	2.589	0.460

¹ SEM: standard error of the mean, ^a,b Means in the same row with different superscripts are significantly different (p < 0.05). ^x,y,z Means of the same parameter in the same column with different superscripts are significantly different (p < 0.05).

shows the results of meat color in rabbits fed diets supplemented with waste avocado paste during days 0, 4, and 8 of maturation. The L* value was higher (p < 0.05) on day 0 in meat from rabbits fed 12.25% AW and lower in the diet with 8.39% AW. The b* and C* values were lower (p < 0.05) on day 0 in meat from rabbits fed 12.25% AW and higher in the control diet.

There was an effect (p < 0.05) of time (days of maturation) on all L*, a*, b*, C*, and H° parameters of meat coloration. The L* color was higher (p < 0.05) on day 0 in all treatments compared to the other days (4 and 8), while for color a*, the values were higher (p < 0.05) on days 0 and 4 in all the treatments vs. day 8. Differences (p < 0.05) were observed in the b* color; values on day 0 of all treatments were lower vs. on days 4 and 8. The C* color was higher (p < 0.05) on day 0 in all treatments compared to the other days (4 and 8). Differences (p < 0.05) were observed in the H° color; values on day 0 of all treatments were lower vs. on days 4 and 8.

3.3. Substance Reactivity to Thiobarbituric Acid (TBARS)

Lipid oxidation during refrigerated storage of rabbit meat led to a continuous accumulation of TBARS, with significant differences (p < 0.05) observed among treatments during day 0, 4, and 8 of refrigeration; the TBARS concentration was significantly lower in the meat of rabbits fed with the diets containing added avocado paste (

Table 5. Lipid oxidative stability (TBARS) in raw meat from rabbits fed diets supplemented with waste avocado paste during day 0, 4, and 8 of refrigeration.

Item	Avocado Waste (% as Feed)				SEM 1	p-Value
	0.00	4.32	8.39	12.25
TBARS (mg MDA/Kg fresh loin)
Day 0	0.34 a,z	0.28 a,z	0.16 b,z	0.14 b,z	0.022		0.001
Day 4	1.09 a,y	0.69 ab,y	0.66 b,y	0.67 b,y	0.105		0.017
Day 8	1.74 a,x	1.37 ab,x	1.15 b,x	1.37 ab,x	0.138		0.036

¹ SEM: standard error of the mean, ^a,b Means in the same row with different superscripts are significantly different (p < 0.05). ^x,y,z Means of the same parameter in the same column with different superscripts are significantly different (p < 0.05).

). In all treatments, on day 8 the meat had the highest TBARS values (p < 0.05) compared to day 4 and lower values on day 0 in all treatments.

3.4. Quantification of the Carbonyl Group of Proteins

Table 6. Oxidative protein stability (DNPH) in raw meat from rabbits fed diets supplemented with waste avocado paste during day 0, 4, and 8 of refrigeration.

Item	Avocado Waste (% as Feed)				SEM 1	p-Value
	0.00	4.32	8.39	12.25
DNPH (nmol carbonyls/mg protein)
Day 0	1.93 a,y	1.18 c,y	1.35 bc,y	1.80 ab,y	0.124	0.008
Day 4	2.07 a,y	2.35 a,x	1.40 b,y	2.52 a,x	0.169	0.004
Day 8	2.43 x	2.44 x	2.15 x	2.78 x	0.236	0.290

¹ SEM: standard error of the mean, ^a,b,c Means in the same row with different superscripts are significantly different (p < 0.05). ^x,y Means of the same parameter in the same column with different superscripts are significantly different (p < 0.05).

shows the protein oxidation of meat from rabbits fed diets with waste avocado paste during day 0, 4, and 8 of refrigeration. On day 0, meat from rabbits fed the control diet had higher levels (p < 0.05) of carbonyls than meat of rabbits fed the 4.32% and 8.39% AW diet, and on day 4, meat from rabbits fed the 8.39% AW diet was lower in carbonyls and higher in carbonyls in meat from rabbits fed the 0, 4.32, and 12.25% AW diets.

With respect to the comparison of the protein oxidation of meat between the different days, significant differences were observed, where there were higher values (p < 0.05) in all treatments on day 8 compared to day 0.

4. Discussion

The potential of natural antioxidants in rabbit meat has been studied, showing a protective effect against lipid and protein oxidation during refrigeration. Wang et al. [21] evaluated the protective effects of Portulaca oleracea L. extract (0.1%, 0.3%, and 0.5% w/w) against lipid and protein oxidation in a period of refrigeration under a rabbit meat patty system for twelve days, determining that it had a protective effect against lipid and protein oxidation (0.1%, 0.3% and 0.5% w/w). They found that as the concentration of the extract decreased, the extent of oxidation increased. However, they also discovered that the use of natural antioxidants could help prevent this oxidation process from occurring.

Selim et al. [22] evaluated the effect of supplementation with Moringa oleifera leaves (5, 10, and 15 g/kg) in weaned rabbits fed for a period of 42 days. The reported results showed that in comparison with the control group, the concentration of PUFA (29.94 vs. 32.45% of total fatty acid) increased in meat from rabbits fed Moringa oleifera leaves, while SFA concentration decreased (41.52 vs. 37.95% of total fatty acid) and malondialdehyde (MDA) content after storage decreased (2.4 vs. 1.5 nmol/g) due to supplementation with Moringa leaves in the diet. Mancini et al. [23] evaluated the effects of the addition of garlic powder (0.25%) and salt (1.00%) on the fatty acid profile and antioxidant potential of rabbit meat patties, reporting a higher amount of PUFA in rabbit meat with added concentration (8.86 vs. 825 mg/100 g), mainly constituted by linoleic acid (C18:2n6), showing a higher antioxidant capacity in meat with garlic added. Therefore, the use of natural antioxidants is recommended as a dietary supplement for rabbits in the final growth stage to increase the nutritional value of the meat.

In the present study, it was found that the addition of avocado paste can modify the fatty acid profile of the Longissimus dorsi muscle of rabbits by decreasing SFA, which was similar to what was found by Hernández et al. [10], where adding avocado paste into pig diets decreased the total SFA. Other studies have mentioned that the addition of sunflower oil, fish oil, and linseed oil can modify the fatty acid profile of the Longissimus dorsi muscle [24]. The composition of fatty acids that are stored in the tissues reflects the lipids that are supplied in the diet offered [25].

Avocado oil may decrease risk factors associated with metabolic syndrome (MS) in rats with sucrose-induced metabolic disorders, reducing triglyceride (TG) and low-density lipoprotein (LDL) and very-low-density lipoprotein (VLDL) levels without changes in high-density lipoprotein (HDL) levels, thus exerting a similar effect to olive oil due to its similar antioxidant content [26,27]. In diabetic rats, Ortíz et al. [28] observed that avocado oil reduced oxidative stress and lipid peroxidation in mitochondria derived from mitochondrial dysfunction, specifically reducing the production of reactive oxygen species, especially at the liver level. The above could be explained by the increase and antioxidant effect of glutathione (GSH) to protect mitochondria from oxidative damage, causing the hypoglycemic effect of avocado oil [29]. In another study, Algarra et al. [30] observed that cheeses made from sheep’s milk enriched with 2% (v/v) of avocado oil showed a lower percentage of SFA and a higher percentage of MUFA and PUFA, as well as lower cholesterol content, compared to traditional Manchego-type cheeses, suggesting that such enrichment could reduce the excess fat intake associated with the consumption of these cheeses.

Likewise, it has been observed that the consumption of avocado seed flour reduces total and LDL cholesterol levels in hypercholesterolemic mice [31]. This effect may be attributed to the phenolic content, its antioxidant activity, and/or the fiber content of the seed. In rats with sucrose-induced insulin resistance, the effect of a standard diet, a standard diet + sucrose, and different standard diets + sucrose + different concentrations of avocado oil (5, 10, 20, and 30%) was measured, finding that there was less weight gain with a higher intake of avocado oil [31]. On the other hand, the area under the curve of the increase in glucose intolerance was lower in the group with the standard diet + sucrose + 5% avocado oil, compared to the group with the standard diet + sucrose [32]. The aqueous extract of avocado seed also had hypoglycemic and tissue protective activity in the pancreas, liver, and kidneys in albino Wistar rats [33].

Luna-Castañeda et al. [34] concluded that meat from sheep fed with avocado flour retains a better color quality under refrigeration, improving oxidative stability processes with extension of the quality and shelf life of meat products, without altering the sensory quality of the meat.

Oxidation of lipids and proteins in meat can cause a rancid odor, bad flavor, and discoloration, affecting the shelf life of the product and consumer acceptance [35]. Meat quality can be evaluated objectively by measuring parameters such as color; consumer preference for meat depends on very important attributes, which are mainly color, texture, and flavor. Wang et al. [36] evaluated the effect of pepper essential oil (0.1%, 0.3%, and 0.5. % w/w) on quality changes in rabbit meat for 12 days under refrigeration, observing that during the last days of storage, lipid oxidation reactions decreased, instead increasing rapidly from day 0 to day 8 in the control treatment; higher hydroperoxide breakdown was observed compared to the pepper essential oil treatments, and they reported that it had a good inhibition effect on lipid and protein oxidation. Similarly, compared to the pepper essential oil treatment, the carbonyl content was higher in the control treatment; the pepper essential oil treatment reduced the rate of color change during the 12 days of rabbit meat storage, decreased the L* and a* values (L* 48 to 35, a* 3 to 0.6), and increased the b* value (b* 11 to 15). It is observed in the present study that L* values were higher on day 0, as well as higher in the treatment with 12.25% avocado paste. It is known that avocado has a green color, which is given by chlorophyll, the main pigment present in the pulp, which could modify the L* value [37]. On the other hand, de Alcantara et al. [38] realized a study comparing the meat color in beef gluteus medius from raised cattle on different days after slaughter (0, 5, and 9) and found a similar color in L* and higher values in b* on day 0 compared to the other days. Faustman et al. [39] have mentioned that discoloration of fresh meat occurs during cold storage and is generally associated with the accumulation of meta myoglobin on the meat surface, and the discoloration process is usually defined as decreased brightness, reddening, and increased yellowness.

Li et al. [40] discussed how molecular mechanisms involved in photosymbiosis can provide information on ROS production, which is crucial for understanding its effect on meat quality. This research shows that adaptations to photosymbiosis may have implications for the stability of meat products, suggesting that genetic diversity in ROS production could influence meat preservation. Likewise, Li et al. [41] emphasize that genome architecture and gene evolution in photosymbiotic organisms may be related to the response to oxidation, indicating that these evolutionary processes could offer valuable insight into how to mitigate oxidation in meat products. This relationship between photosymbiosis and lipid and protein stability may help to develop more effective strategies for meat preservation using natural antioxidants that modulate ROS production and improve product shelf life.

The discoloration of chilled meat is usually related to the occurrence of lipid oxidative reactions [38,42,43]. In the present work the discoloration was greater in rabbit meat on day 8 than day 0 and 4 with 32% avocado paste inclusion, which may be due to a higher accumulation of Schiff pigments from lipid to protein complexes in this treatment as a result of oxidative stress [44], which was a similar result to pigs fed avocado paste, which presented lower lipid oxidation rates and less intense discoloration during cold storage than those not fed avocado [10].

There is now increasing evidence indicating that waste avocado fruit included in the diet of livestock species improves certain beneficial health attributes in the meat, primarily in the prevention of risk factors such as dyslipidemia, glycemia, and hypertension. However, studies carried out in animal models will need to be confirmed with clinical studies in humans.

Future research should emphasize the effects of consuming products such as meat and milk from animals fed avocado (pasta, flour, oil, etc.) on conditions such as osteoarthritis, DNA damage, blood pressure, iatrogenic and teratogenic indices, and visual health, among others.

5. Conclusions

The addition of waste avocado paste at 12.25% in the diet for rabbits was better; it increased the content of n-3 polyunsaturated fatty acids and protected the meat from the products of lipid and protein oxidation from 0 to 8 days, decreasing discoloration and delaying oxidation during their maturation, resulting in meat with a longer shelf life.