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Article

Fermentation of Dietary Fibre-Added Milk with Yoghurt Bacteria and L. rhamnosus and Use in Ice Cream Production

by
Elif Sezer
*,
Ahmet Ayar
and
Suzan Öztürk Yılmaz
Department of Food Engineering, Faculty of Engineering, Sakarya University, Serdivan 54187, Turkey
*
Author to whom correspondence should be addressed.
Fermentation 2023, 9(1), 3; https://doi.org/10.3390/fermentation9010003
Submission received: 30 November 2022 / Revised: 18 December 2022 / Accepted: 19 December 2022 / Published: 21 December 2022
(This article belongs to the Special Issue Dairy Fermentation)
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Abstract

:
This study investigated whether the use of fermented milk with added dietary fibre in ice cream production positively affected quality characteristics, especially viability, during a shelf life of 90 days at −25 °C. For this purpose, fermented milk was prepared with cultures (yoghurt and Lacticaseibacillus rhamnosus) and dietary fibre (wheat fibre and inulin). In addition to the viable cell count, some related quality characteristics, such as the sensory, physical, chemical, and thermal properties, and energy content were also examined. Streptococcus salivarius subsp. thermophilus in all yoghurt ice creams and L. rhamnosus in ice cream with wheat fibre had the highest viability for 90 days, up to 95.95%. The best scores regarding “general acceptability” belonged to the ice cream with L. rhamnosus and inulin, with a score of 7.81 out of 9. The dietary fibre decreased overrun from around 23% to 14–18%, which was positive for the viability of the cultures. The cultures and dietary fibre decreased the melting temperature down to −1.15 °C. The caloric value of the ice creams (166–168 kcal/100 g) was lower than that of standard ice cream. Probiotic ice cream production with dietary fibre and a single L. rhamnosus culture may be preferred in terms of sensory properties, cell viability, and economic aspects.

Graphical Abstract

1. Introduction

Functional food components have some benefits in the natural prevention of diseases, such as gastrointestinal problems, obesity, high cholesterol, and diabetes. Therefore, bioactive compounds, probiotic microorganisms, and prebiotic substances are often used to add functional properties to foods. Dairy products, such as ice cream and yoghurt, are one of the most suitable foods in terms of adding functional properties. The fat content of such dairy products can be easily reduced and enriched with bioactive compounds [1,2]. Various functional components have been used in the production of ice cream and yoghurt, and their effects on product quality have been investigated. Al et al. [1] used recombinant microbial transglutaminase enzyme and Zagorska et al. [3] used lactobionic acid in ice cream production. Akpınar et al. [4] produced yoghurts with the addition of probiotics (Enterococcus faecium and Enterococcus durans), while Molaee Parvarei et al. [5] produced yoghurt with the addition of parabiotics (killed probiotic cells).
Probiotics, meaning ‘for life’ in Greek, are important functional food ingredients [6]. Probiotics are considered ‘live microorganisms that, when administered in adequate amounts, confer a health benefit on the host’ according to the definition of the WHO and FAO in 2002 [7]. The common recommendation for adequate amounts is 6–7 log cfu/mL or g [8]. Due to the increasing worldwide demand every year, the global ice cream market is expected to increase by 37% over a 6-year period, from USD 71.52 billion in 2021 to USD 97.85 billion in 2027 [9]. Ice cream, which has a high consumption rate worldwide, provides a very suitable probiotic carrier due to its rich composition [8,10]. Numerous studies have examined the effects of probiotics on the quality and health benefits of ice cream and emphasized the importance of ice cream as a probiotic carrier. Consumption of probiotic ice cream has a positive effect on intestinal ecology and oral health [8].
Due to its prebiotic properties, dietary fibre is generally reported to have a positive effect on yoghurt and probiotic cultures. In recent years, there have been various studies on yoghurt and probiotic ice creams with dietary fibre added. While some studies examining the effect of dietary fibre on the viability of various cultures in ice cream indicated a positive effect of dietary fibre on viable cell count, some other studies reported no such effect. Akalın et al. [11] stated that wheat fibre (2%) promoted the number of live Bifidobacterium animalis subsp. lactis in ice cream samples. Di Criscio et al. [12] reported that inulin increased the number of total lactic acid bacteria (Lacticaseibacillus casei and Lacticaseibacillus rhamnosus) in probiotic ice creams. It was also stated that the probiotic bacteria (Lactobacillus acidophilus and Bifidobacterium lactis) survival rate was higher in probiotic ice creams with inulin than those without inulin. Additionally, inulin improved the viscosity and first dripping and complete melting times, without changing the sensory properties [13]. In contrast, Hashemi et al. [14] reported that inulin had no protective effect on Lactobacillus acidophilus during 90 days of storage in probiotic ice creams. Nevertheless, the effects of dietary fibre in both fermented milk and ice creams derived from fermented milk have not been studied in detail, including the sensory, physical, chemical, and thermal properties of ice cream.
Yoghurt bacteria (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus) are frequently used in culture-added (yoghurt and probiotic) ice cream formulations. S. thermophilus is known to have good endurance against harsh conditions, which is related to the fatty acid composition of the cell membrane [15]. On the other hand, S. thermophilus has weak proteolytic activity; it cannot produce the amino acids necessary for its growth. L. bulgaricus, on the other hand, can produce the amino acids required for S. thermophilus by producing free amino acids from casein fractions. Formic acid and CO2, which are necessary for the development of L. bulgaricus, are also formed by S. thermophilus. For this reason, these two bacteria are often used together [16,17]. L. rhamnosus GG (LGG) was isolated from the digestive system of a healthy person in 1983. In recent years, L. rhamnosus has become a probiotic bacterium that has attracted attention due to its various properties and it is beginning to be frequently used in studies [18,19]. L. rhamnosus can survive at a higher rate in the freezing medium than L. acidophilus. Therefore, L. rhamnosus is an advantageous probiotic for ice cream [20]. However, it has been used in limited studies on yoghurt and probiotic ice creams [12,20,21]. The production steps of ice cream may impair the viability of cultures. The most important steps to be evaluated are overrun, freezing, and frozen storage. Thus, it is necessary to study their impact carefully [8,22,23].
This study aimed to examine the effect of dietary fibre (wheat fibre and inulin) on the viable cell count in milk fermented with yoghurt bacteria and L. rhamnosus and in ice creams derived from this milk. In addition, the effects of cultures and dietary fibre on the sensory, physical, chemical, and thermal properties of the ice creams were also investigated.

2. Materials and Methods

2.1. Materials

Yoghurt bacteria (L. bulgaricus and S. thermophilus, Y401, Maysa, Tuzla, İstanbul, Turkey) and L. rhamnosus LGG (Chr. Hansen, Hoersholm, Denmark) were used as the cultures in the formulations. The other ingredients included: UHT milk (3.3% fat, Torku), skim milk powder (Bağdat Baharat), cream (35% fat, İçim), crystallised granulated sugar (from sugar beet, Nehir), stabiliser (50% carboxymethyl cellulose, 25% guar gum, and 25% xanthan gum, Smart Kimya, Tito BUZ 200), emulsifier (90% glycerol monostearate, Hangzhou Fuchun Food Additive Co. Ltd., Hangzhou, China), wheat fibre (Jelucell Wheat Fiber 90, Jelu-Werk, Rosenberg, Germany), inulin (Fibrelle, Çekmeköy, İstanbul, Turkey). PET containers (20 and 50 mL) with lids (Özge Plastic, Arnavutköy, İstanbul, Turkey) were used for packaging.

2.2. Preparation of Fermented Milk

In the preparation of cultures, lyophilized yoghurt (L. bulgaricus and S. thermophilus) and L. rhamnosus GG cultures were first inoculated separately in sterile skimmed milk at a rate of 0.3% (3 g/L). The mother culture was obtained by fermentation of this prepared milk. The bulk culture was propagated by the mother culture (5%, w/w). After fermentation, the mother and bulk cultures had bacterial counts of approximately 8.4–8.8 log cfu/mL. The fermented milk samples with and without fibre were inoculated with the bulk culture (5%, w/w). The yoghurt and L. rhamnosus cultures were incubated at 42 °C and 37 °C, respectively.
The dietary fibre was added to the milk at a rate of 5% (w/w), with a final composition of 1.5% (w/w) in the ice creams. To prevent precipitation, 0.1% (w/w) stabiliser was added to the milk prepared with wheat fibre. This stabiliser ratio did not affect bacterial growth. The milk samples with and without fibre were pasteurised at 75 ± 2 °C for 30 min. The samples inoculated with the yoghurt (5%) and L. rhamnosus (5%) cultures were incubated for 3–3.5 h at 43 ± 2 °C and 3.5–4 h at 37 ± 2 °C, respectively. The incubation was continued until the pH reached 4.7, and the samples were taken to the refrigerator and rested for 2–3 h until ice cream production.

2.3. Preparation of Yoghurt and Probiotic Ice Creams

The 70 g mix contained 35.4 g milk, 10.0 g milk cream, 11.0 g milk powder, 13.0 g sugar, 0.3 g stabiliser, and 0.3 g emulsifier. The solid ingredients (milk powder, sugar, stabiliser, and emulsifier) were added to the liquid ingredients (milk and milk cream), heated to 45–50 °C, and mixed. The mix was pasteurised at 75 ± 2 °C for 30 min, cooled to 4 ± 2 °C, and then left to mature for 24 h. Before the samples were taken to the ice cream machine, fermented milk (30%, w/w) was mixed with the mix (70%, w/w). The prepared mixture was transferred to the ice cream machine (Delonghi, ICK 5000) and processed for approximately 30 min. The process was completed when the mix temperature decreased to −6 ± 1 °C. Then, the samples were packed and stored at −25 °C. Figure 1 shows the design and composition of the ice cream samples.

2.4. Determining the Quality Properties of Yoghurt Ice Creams

2.4.1. Viable Cell Counts of Yoghurt and Probiotic Bacteria

The viable cell count of L. bulgaricus and L. rhamnosus was determined using MRS agar, and the petri dishes were incubated for 48–72 h under anaerobic conditions with Anaerocult A (Merck) at 37 °C. In the enumeration of S. thermophilus, M17 agar was used, and the petri dishes were incubated at 37 °C for 48 h under aerobic conditions [24,25]. The results were expressed as log cfu/g and % viability (Equation (1)).
Viability (%) = ([log cfu/g (last))/(log cfu/g (initial)]) × 100

2.4.2. Sensory Evaluation

The sensory evaluation was carried out with nine semi-trained academic staff and students of Sakarya University. Regarding “elongation in the spoon”, “iciness”, “degree of sweetness”, “degree of sourness”, and “melting time in the mouth” features, values between 6–9 points were above average, 5 points were average, and 1–4 points were below average. A rating of “0” meant that the feature was absent. In terms of “colour and appearance”, “structure and consistency”, “taste and smell”, and “general acceptability” characteristics, 9 points were defined as “excellent”, 5 points as “average”, and 1 point as “very poor”. The sensory analyses were carried out one week after each production [26].

2.4.3. Analysis of Physical Properties

The viscosity of the ice creams was measured at 5 ± 2 °C using a Fungilab Alpha H (Spain) viscometer with the R2 spindle at 60 rpm [27]. The overrun was calculated according to Equation (2) by measuring the mass of a certain amount of ice cream before and after melting [28]:
Overrun (%) = [(Mix mass − Ice cream mass)/Ice cream mass] × 100
For the melting test, 20 ± 0.5 g sample was left to melt at 20 ± 2 °C on a wire mesh with 3 × 3 mm2 pore area. The times for the first dripping and complete melting were recorded [29]. The hardness (g) of the sample was determined using the Brookfield CT3-4500 texture analyser and the TA39 probe. The other parameters included: pre-test speed of 2 mm/s, test speed of 2 mm/s, rotation speed of 2 mm/s, penetration distance of 10 mm, holding time of 5 s, and trigger load of 4.5 g [30]. The temperature of the sample was brought to −10 ± 2 °C and maintained at this temperature for a day before the measurement. The fat destabilization (%) that occurred during the ice cream formation from the mix was determined using a spectrophotometric method based on the procedure described by Rossa et al. [31]. The mixes and melted ice creams were diluted 1:500 (v/v) with distilled water and centrifuged at 1000 rpm for 5 min. After 10 min, the absorbance was measured at 540 nm. The absorbance of the pure water used in dilution was measured as a blank sample. The calculation of the measurement results was made according to Equation (3):
Fat destabilization (%) = [(Amix − Aice cream)/Amix] × 100

2.4.4. Analysis of Chemical Properties

The pH was measured using a calibrated digital pH meter (Hanna Instruments, pH 211, Weilheim, Germany) at 20 ± 2 °C. The acidity of the sample as lactic acid was determined using the titration method (AOAC 947.05) with 0.1 N NaOH. The gravimetric method (AOAC 941.08) was used to determine the total solids content (%), and the Gerber method (AOAC 2000.18) was used to determine the fat content (%) of the ice creams [32].

2.4.5. Analysis of Thermal Properties

The analysis was performed according to the method described by Kavaz Yuksel [33] with some modifications. Approximately 15 mg of ice cream was weighed into an aluminium DSC pan and then loaded into the DSC instrument (Seiko DSC 7020, Hitachi High-Tech Co., Tokyo, Japan) at 25 °C. An empty pan was used as a reference, and the procedure was followed, including the following steps: (1) cooling from 25 °C to −80 °C at 10 °C/min; (2) annealing at −80 °C for 15 min; (3) heating from −80 to 25 °C at 10 °C/min, (4) holding at 25 °C for 1 min. The melting (Tm) and glass transition (Tg) temperatures were determined from the spectrum obtained.

2.4.6. Energy (Calorie) Content

The caloric content of the ice creams was calculated by multiplying the fat content by 9 kcal/g and multiplying the carbohydrate and protein contents by 4 kcal/g [34].

2.4.7. Statistical Analysis

The ice cream samples were produced in triplicate. The microbiological, physical, and chemical analyses were performed on two replicates from each production. Sensory evaluation was performed on each production. One-way analysis of variance was used to analyse the data using IBM SPSS 20.0 (IBM Corp., Armonk, NY, USA). Duncan’s multiple range test was used to assess differences among means (p < 0.05). The sensory analysis data were evaluated using the Kruskal-Wallis H test and the Mann-Whitney U test was used to assess differences among means.

3. Results and Discussion

3.1. Viable Cell Counts

The viable cell counts of L. bulgaricus, S. thermophilus, and L. rhamnosus in the fermented milk and the change in the viable cell counts of the ice creams for 90 days are shown in Table 1; the % viability of the cells calculated using the viable cell counts is given in Table 2. While the wheat fibre did not contribute to the number of L. rhamnosus, it had a promoting effect on the number of L. bulgaricus and S. thermophilus in the fermented milk.
Some studies have reported that wheat extracts significantly protected the viability of Lactiplantibacillus plantarum, L. acidophilus, and Lactobacillus reuteri in culture media under acidic conditions. This protective effect was associated with the amount of sugar in the wheat extracts [35]. Additionally, wheat fibre (2%) was shown to promote the viable counts of B. lactis in ice cream samples [11]. However, the addition of inulin did not significantly affect the counts of L. bulgaricus, S. thermophilus, and L. rhamnosus in fermented milk. Similarly, Akalın and Erişir [36] indicated that inulin did not affect the counts of L. acidophilus and B. animalis BB-12. On the contrary, Akin et al. [13] mentioned the positive effect of 1–2% inulin on the viability of L. acidophilus and B. lactis in ice creams for 90 days. Moreover, the same study indicated that inulin did not affect the counts of S. thermophilus and L. bulgaricus during storage. Carbohydrates in dietary fibre can be selectively fermented by various probiotic bacteria and used as an energy source. Factors such as culture type, dietary fibre type and amount, and storage temperature affect the interaction between dietary fibre and cultures [11,13,35,36].
Although ice cream is a suitable product for probiotic bacteria, freezing can cause a loss of up to 1 log in the viable bacteria count. Possible factors causing a reduction in the viable cell count during the processing of the mix into ice cream include injury of cells by freezing, mechanical stress during mixing, and integration of oxygen into the mix [22,37,38,39]. The most resistant culture to the freezing process from mix to ice cream was S. thermophilus, whereas L. bulgaricus was the most vulnerable. This resistance of S. thermophilus to cold conditions is related to the fatty acid composition of the cell membrane [15]. The viable cell count of S. thermophilus in the ice creams without dietary fibre was not changed during the processing of the mixes into ice creams. In contrast, a decrease in the viable cell count was observed in ice creams with dietary fibre during this process. The viable cell counts decreased in all samples during 90 days of storage. S. thermophilus and L. rhamnosus showed higher % viability during storage than L. bulgaricus. The decrease of L. bulgaricus count and the durability of S. thermophilus during 90 days with counts above 10⁷ log cfu/g was reported similarly in the study by Akın et al. [13]. An optimum level of initial viable probiotics is one of the key points to ensuring the limit bacterial count (>6 log cfu/g) until the end of at least 90 days of storage [8,39]. There is no universally accepted framework for regulating probiotics, so it differs between countries. However, for a food to be called a probiotic food, the number of living cells is generally required to be at least 6 or 7 log cfu/mL or g. Similar numbers are also valid for yogurt bacteria. These values are accepted in various national and regional regulations [40,41]. In addition to the cell count of the probiotic food per g or mL, the consumption amount is also important to achieve therapeutic effects. A minimum therapeutic daily dose of 8–9 log cfu, corresponding to 100 g of a food product containing 6–7 log cfu/g, has been suggested to induce beneficial probiotic effects [6,42].

3.2. Sensory Evaluation

Table 3 shows the sensory scores of the ice creams. There was no statistical difference among ice cream samples regarding “elongation in spoon”, “iciness”, “degree of sweetness”, “degree of sourness”, “melting time in mouth”, or “colour and appearance” scores (p > 0.05). The most liked ice creams in terms of “structure and consistency” were fibre-free yoghurt ice cream and probiotic ice cream with inulin.
It is known that the acidic taste of yoghurt and probiotic ice creams slightly reduces the sensory acceptance, mainly the taste; additionally, it is reported that an acidic aroma is observed at pH 5.6 and flavourings can mask acidic off-flavours [8,38,43]. In this study, such an effect was not observed due to the low acidity of the yoghurt and probiotic ice creams, although no flavouring was used.
The probiotic ice cream with inulin had the highest scores in terms of “taste and smell” and “general acceptability”, whereas the yoghurt ice cream with wheat fibre had the lowest scores in terms of these parameters. No physical or chemical properties were found that could be positively or negatively related to the “structure and consistency”, “taste and smell”, and “general acceptability” scores in ice creams.
In addition, there was no difference in the number of L. rhamnosus between the most-liked probiotic ice cream with inulin and the other probiotic ice creams. In this case, some aroma compounds formed by L. rhamnosus using inulin may have positively affected the related scores. It has been reported that inulin can improve the metabolic activity of some Lactobacillus strains, thus providing different volatile compounds in fermented milk [22]. The number of S. thermophilus in the least-liked ice cream was higher than that in the other yoghurt ice creams. The aroma compounds formed by a higher number of S. thermophilus may have decreased the sensory satisfaction [44].

3.3. Physical and Chemical Properties

Table 4 shows the physical properties of the ice creams on the first day of storage. As expected, adding culture and fibre increased the viscosity of the yoghurt and probiotic ice cream samples. Applying a certain amount of air (overrun) to the ice cream mix, thus increasing the oxygen level, creates a critical problem for probiotic bacteria with anaerobic and microaerophilic properties [45]. For this reason, preserving the viable cell count may be appropriate by keeping the overrun low. While yoghurt and L. rhamnosus cultures did not affect the % overrun, dietary fibre decreased the % overrun, possibly positively affecting the viable cell counts. However, this study did not observe a direct relationship between overrun and viability due to other factors that may affect viability.
A low fat content in ice cream accelerates melting, while a low sugar content, on the hand, has a retarding effect on melting. In this instance, low sugar and fat levels balanced each other in melting ice cream [33,46]. Akalın et al. [11] reported that wheat fibre-added ice cream melted later than ice cream without fibre. Similarly, wheat fibre increased the first dripping times but decreased the complete melting times in yoghurt and probiotic ice creams in this study. Inulin was expected to delay dissolution due to its ability to bind the free movement of water molecules, which is related to its stabiliser effect [13]. However, 1.5% inulin did not affect the first dripping times but slightly reduced the complete melting times in this study. The addition of yoghurt cultures and wheat fibre increased the hardness of the ice creams, whereas L. rhamnosus and inulin had no effect.
The consistency of milk increases with fermentation. Thus, the addition of fermented milk was expected to increase the hardness of ice creams. However, similar to the effect of adding L. rhamnosus, adding milk fermented with Lacticaseibacillus casei-01 did not significantly affect the hardness. In addition, it is reported that the low soluble matter content of dietary fibre provides high water retention and therefore causes an increase in viscosity, consistency, and the hardness index in ice creams. However, this effect of dietary fibre on hardness may sometimes be statistically insignificant in ice creams [8,11,22].
The whipping and freezing processes transform some fat in the mix into a three-dimensional aggregated fat structure. This transformation, which provides structural integrity, is known as fat destabilisation. An increase in partially coalesced globule clusters indicates a higher degree of fat destabilization during freezing. The presence of these clusters has a positive and significant effect on the physical properties of ice cream, especially on melting. The advanced structure of the foam caused by the fat network formed during fat destabilisation provides a soft ice cream with good melting resistance. Insufficient destabilisation leads to poor shape retention and rapid melting. At the same time, too much destabilisation can result in the formation of visible fat granules and ice cream that does not melt in a reasonable time at consumption temperatures. Whipping and freezing must occur at the same time to create the desired fat destabilisation. Emulsifiers increase fat destabilisation, thereby providing increased physical stabilization [31,34]. Fat destabilisation (%) was found to be higher in culture-added fibre-free ice creams than in the other ice creams. Moreover, dietary fibre decreased the fat destabilisation (%) of the ice creams. The “melting time in the mouth” scores were found to be ‘average’ in the sensory evaluation. In this case, it can be concluded that the low % fat destabilisation of ice creams did not adversely affect the sensory melting properties. Bolliger et al. [47] found that ice creams containing a lower percentage of destabilised fat had faster melting rates. Many researchers have noted that an increased level of destabilised fat increases the hardness of ice creams, but an increased level of overrun has an inverse effect on hardness [46]. For the ice creams in this study, low fat destabilisation and overrun rates may have had a balanced effect on hardness.
The chemical properties of the ice creams on the first day of storage are shown in Table 4. The pH and % lactic acid values of the control ice cream were 6.56 and 0.21%, respectively, while the yoghurt and probiotic ice creams had 6.23–6.28 pH and 0.32–0.38% lactic acid. In the literature, the pH of cultured ice creams is generally determined to be 5.0–6.0, while standard ice cream has a pH near 6.5 [11,48]. The acidity of the ice creams with yoghurt culture and L. rhamnosus was lower than the values mentioned. It is known that higher acidity has a negative effect on viability during storage. For this reason, it is assumed that the balanced acidity of ice creams had a positive effect on the viability of the cultures. In addition, mild acidity often improves the sensory quality of yoghurt and probiotic ice creams. The addition of dietary fibre slightly increased the total solids content (%) of the ice creams, as expected. The total amount of solids is one of the factors that directly affects the viscosity of the mixture and the hardness of the ice cream. An increase in the amount of dry matter also increases the viscosity and hardness. The ice cream samples could be classified as light, with 5.82–5.98% fat content. Fat has a positive effect on ice cream’s physical stabilisation and melting properties. A decreased amount of fat causes faster melting, and it may be necessary to balance lower fat content with another factor that will delay the melting time [8,34].

3.4. Thermal Properties

The melting temperatures (Tm) were between −1.15 and 1.88 °C, and the glass transition temperatures (Tg) were between −30.72 and −28.31 °C in all ice creams. Tm decreased with culture and dietary fibre. There was no change in the Tg (Table 5). The melting of ice cream starts around −3 °C. Sweeteners dissolve and lower the mixture’s freezing point [34,46]. While a typical frozen yoghurt composition contains 15% sugar, this study used 13% sugar. For this reason, the decrease in sugar content may have increased the melting temperature. It is recommended to store ice cream below the Tg to maintain the best stability; the higher the storage temperature above the Tg, the greater the deterioration in stability [34,49]. Many commercial ice creams have a Tg below −32 °C, but storage at such low temperatures is not commercially feasible. Furthermore, a storage condition at or below −25 °C can give a sufficiently slow recrystallisation rate to support extended shelf life [34]. In this study, the difference between the Tg and the storage temperature decreased because the Tg of the ice creams was slightly higher than that of commercial ice creams, indicating the stability could be better preserved during frozen storage.

3.5. Energy (Calorie) Content

The energy content of the ice cream mixes was 166 kcal/100 g for the control, yoghurt, and probiotic ice creams without dietary fibre and 168 kcal/100 g for the ice creams with dietary fibre. The caloric content of the ice cream samples was lower than that of a standard ice cream, which is approximately 200 kcal/100 g [50].

4. Conclusions

Wheat fibre promoted the best viability of L. rhamnosus for 90 days of storage at −24 °C. The probiotic ice cream (L. rhamnosus) with inulin had the highest “taste and smell” and “general acceptability” scores, at 7.93 and 7.81, respectively. In addition, 93.72% viability of L. rhamnosus was observed in this sample after 90 days of storage. Production of yoghurt and probiotic ice creams without flavourings and providing above 6 log cfu/g viable cell count with a single culture of L. rhamnosus can be an economical option. Future studies on fermented ice creams may prefer simpler methods using fermented flavour in a positive way rather than masking it. In addition, dietary fiber types and amounts can also be studied. Adding more dietary fibre to the mix can provide a noticeable change in the physical properties. Moreover, changes in aroma compounds and their relationship with the sensory properties can be examined by adding wheat fibre and inulin to yoghurt and L. rhamnosus.

Author Contributions

Conceptualization, E.S., A.A. and S.Ö.Y.; Methodology, E.S., A.A. and S.Ö.Y.; Validation, E.S., A.A. and S.Ö.Y.; Formal analysis, E.S.; Investigation, E.S., A.A. and S.Ö.Y.; Resources, E.S.; Data curation, E.S.; Writing—original draft preparation, E.S.; Writing—review and editing, E.S., A.A. and S.Ö.Y.; Supervision, A.A.; Project administration, A.A.; Funding acquisition, A.A. All authors have read and agreed to the published version of the manuscript.

Funding

This study was funded by Scientific Research Projects Unit of Sakarya University (Grant No: 2020-7-25-36).

Institutional Review Board Statement

Sakarya University Ethics Committee reviewed the plan of this study and the committee found that the ice cream samples were suitable for human sensory evaluation (06/04/2020-E.3964).

Informed Consent Statement

Not applicable.

Data Availability Statement

Not applicable.

Acknowledgments

The authors acknowledge the financial support of Scientific Research Projects Unit, Sakarya University, for the PhD study of Elif Sezer. The authors also thank Hansen (Kadıköy, İstanbul, Turkey), Tunçkaya Chemicals (Tuzla, İstanbul, Turkey), and Jelu-Werk (Ludwigsmühle, Rosenberg, Germany) for donating materials.

Conflicts of Interest

The authors declare no conflict of interest.

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Fermentation 09 00003 g001 550
Figure 1. The experimental design of yoghurt and probiotic ice creams.
Figure 1. The experimental design of yoghurt and probiotic ice creams.
Fermentation 09 00003 g001
Table
Table 1. Viable cell count of L. bulgaricus, S. thermophilus, and L. rhamnosus in the yoghurt and probiotic ice creams during storage (log cfu/g).
Table 1. Viable cell count of L. bulgaricus, S. thermophilus, and L. rhamnosus in the yoghurt and probiotic ice creams during storage (log cfu/g).
Sample Fermented MilkMixDay 1Day 30Day 60Day 90
YL. bulgaricus8.41 ± 0.06 DE7.64 ± 0.05 Ea7.21 ± 0.07 Db7.09 ± 0.09 Fc6.91 ± 0.14 Ed6.72 ± 0.10 De
Y-WF8.56 ± 0.05 C7.67 ± 0.03 DEa7.21 ± 0.07 Db7.11 ± 0.07 EFc7.00 ± 0.08 Ed6.78 ± 0.11 De
Y-INU8.43 ± 0.05 D7.41 ± 0.05 Fa7.20 ± 0.09 Db7.19 ± 0.06 Eb7.13 ± 0.08 Db6.80 ± 0.11 Dc
YS. thermophilus8.84 ± 0.06 B8.41 ± 0.05 Ba8.42 ± 0.11 ABa8.33 ± 0.11 Aab8.20 ± 0.13 Bb8.00 ± 0.11 Bc
Y-WF8.97 ± 0.06 A8.56 ± 0.04 Aa8.46 ± 0.09 Aab8.41 ± 0.09 Abc8.32 ± 0.07 Ac8.21 ± 0.13 Ad
Y-INU8.88 ± 0.06 B8.43 ± 0.05 Ba8.32 ± 0.13 Bab8.22 ± 0.10 Bbc8.17 ± 0.12 Bc7.98 ± 0.10 Bd
LRL. rhamnosus8.37 ± 0.09 DE7.81 ± 0.08 Ca7.59 ± 0.03 Cb7.40 ± 0.06 Dc7.40 ± 0.09 Cc7.31 ± 0.09 Cc
LR-WF 8.34 ± 0.05 E7.72 ± 0.06 Da7.51 ± 0.09 Cb7.51 ± 0.08 Cb7.46 ± 0.07 Cbc7.39 ± 0.06 Cc
LR-INU8.38 ± 0.08 DE7.79 ± 0.06 Ca7.61 ± 0.10 Cb7.39 ± 0.04 Dc7.34 ± 0.10 Cc7.30 ± 0.09 Cc
Mean (n = 6) ± standard deviation. Different capital letters indicate significant differences among the ice creams, and different lowercase letters indicate significant differences among storage periods (Duncan’s test, p < 0.05). Y = ice cream with yoghurt culture, Y-WF = ice cream with yoghurt culture and wheat fibre, Y-INU = ice cream with yoghurt culture and inulin, LR = ice cream with L. rhamnosus, LR-WF = ice cream with L. rhamnosus and wheat fibre, LR-INU = ice cream with L. rhamnosus and inulin.
Table
Table 2. Viability (%) of bacteria in the yoghurt and probiotic ice creams during storage.
Table 2. Viability (%) of bacteria in the yoghurt and probiotic ice creams during storage.
Sample Day 1Day 30Day 60Day 90
YL. bulgaricus94.44 ± 1.33 Ca92.85 ± 1.38 Da90.42 ± 1.60 Db87.92 ± 1.66 Dc
Y-WF94.05 ± 1.42 Ca92.77 ± 1.30 Dab91.27 ± 1.44 Db88.47 ± 1.81 Dc
Y-INU97.19 ± 0.69 Ba97.04 ± 1.33 Ba96.21 ± 1.48 ABa91.81 ± 1.44 Cb
YS. thermophilus100.13 ± 1.64 Aa99.00 ± 1.44 Aab97.53 ± 1.72 Ab95.11 ± 1.07 ABc
Y-WF98.81 ± 1.15 ABa98.29 ± 1.29 ABab97.24 ± 0.52 Abc95.95 ± 1.65 Ac
Y-INU98.64 ± 1.39 ABa97.48 ± 1.35 ABab96.84 ± 1.03 Ab94.62 ± 0.74 ABc
LRL. rhamnosus97.18 ± 1.65 Ba94.76 ± 1.13 Cb94.74 ± 1.10 BCb93.57 ± 1.92 Bb
LR-WF97.30 ± 1.19 Ba97.31 ± 1.32 Ba96.63 ± 0.67 Aab95.81 ± 0.77 Ab
LR-INU97.66 ± 1.99 Ba94.87 ± 1.22 Cb94.24 ± 1.99 Cb93.72 ± 1.73 Bb
Viability (%) was calculated by assuming that the mixes had 100% viability of the cultures. Mean (n = 6) ± standard deviation. Different capital letters indicate significant differences among the ice creams, and different lowercase letters indicate significant differences among storage periods (Duncan’s test, p < 0.05). Y = ice cream with yoghurt culture, Y-WF = ice cream with yoghurt culture and wheat fibre, Y-INU = ice cream with yoghurt culture and inulin, LR = ice cream with L. rhamnosus, LR-WF = ice cream with L. rhamnosus and wheat fibre, LR-INU = ice cream with L. rhamnosus and inulin.
Table
Table 3. Sensory scores of the yoghurt and probiotic ice creams.
Table 3. Sensory scores of the yoghurt and probiotic ice creams.
SampleElongation at SpoonIcinessDegree of SweetnessDegree of SournessMelting Time in MouthColour and AppearanceStructure and ConsistencyTaste and SmellGeneral
Acceptability
C4.81 ± 1.39 A1.79 ± 1.89 A5.53 ± 0.84 A2.94 ± 2.02 A5.02 ± 1.09 A7.93 ± 0.97 A7.22 ± 1.03 AB7.38 ± 1.03 AB7.33 ± 1.04 ABC
Y4.44 ± 1.78 A1.67 ± 0.88 A5.19 ± 1.00 A4.15 ± 2.20 A5.30 ± 1.14 A8.00 ± 0.88 A7.56 ± 1.05 A7.44 ± 1.01 AB7.44 ± 1.05 AB
Y-WF4.11 ± 1.69 A1.89 ± 1.12 A5.07 ± 0.92 A4.15 ± 2.23 A5.19 ± 1.21 A7.85 ± 1.13 A6.74 ± 1.63 B6.44 ± 1.22 C6.78 ± 1.19 C
Y-INU4.74 ± 1.70 A1.56 ± 0.89 A5.44 ± 1.01 A3.85 ± 2.11 A5.22 ± 1.01 A7.93 ± 1.04 A7.41 ± 1.15 AB7.04 ± 1.19 B7.15 ± 1.06 BC
LR4.19 ± 1.75 A1.74 ± 0.94 A5.15 ± 1.17 A3.19 ± 2.15 A5.04 ± 1.29 A8.07 ± 0.87 A7.22 ± 1.19 AB7.59 ± 1.05 AB7.70 ± 0.78 AB
LR-WF4.37 ± 1.67 A1.33 ± 0.78 A5.44 ± 1.12 A3.89 ± 2.22 A5.44 ± 1.12 A7.81 ± 1.08 A6.81 ± 1.78 AB7.22 ± 1.12 B7.30 ± 1.17 ABC
LR-INU4.85 ± 1.92 A1.93 ± 1.00 A5.44 ± 1.25 A3.30 ± 2.20 A5.19 ± 1.39 A8.11 ± 0.70 A7.56 ± 1.15 A7.93 ± 0.78 A7.81 ± 0.79 A
Mean (n = 6) ± standard deviation. Different letters in the same column indicate significant differences among the ice creams (Duncan’s test, p < 0.05). C = control, Y = ice cream with yoghurt culture, Y-WF = ice cream with yoghurt culture and wheat fibre, Y-INU = ice cream with yoghurt culture and inulin, LR = ice cream with L. rhamnosus, LR-WF = ice cream with L. rhamnosus and wheat fibre, LR-INU = ice cream with L. rhamnosus and inulin.
Table
Table 4. Physical and chemical properties of the yoghurt and probiotic ice creams on the first day of storage.
Table 4. Physical and chemical properties of the yoghurt and probiotic ice creams on the first day of storage.
PropertiesCYY-WFY-INULRLR-WFLR-INU
Viscosity (Pa.s)1.08 ± 0.07 d2.28 ± 0.06 c2.77 ± 0.03 a2.69 ± 0.05 a2.30 ± 0.09 c2.57 ± 0.09 b2.53 ± 0.10 b
Overrun (%)22.6 ± 1.8 a22.9 ± 2.0 a15.5 ± 2.2 bc17.9 ± 2.8 b22.8 ± 2.9 a13.6 ± 3.8 c16.1 ± 2.3 bc
First dripping (sec)1998 ± 34 b2053 ± 43 b2183 ± 49 a1992 ± 44 b2007 ± 48 b2213 ± 42 a2018 ± 70 b
Complete melting (sec)3311 ± 55 a3078 ± 30 c3017 ± 65 cd2987 ± 43 d3259 ± 70 ab3326 ± 79 a3225 ± 71 b
Hardness (N)1.20 ± 0.11 c1.53 ± 0.10 b1.78 ± 0.17 a1.49 ± 0.15 b1.22 ± 0.11 c1.44 ± 0.12 b1.23 ± 0.09 c
Fat destabilisation (%)12.76 ± 0.55 f21.81 ± 0.85 b17.49 ± 0.48 d10.39 ± 0.55 g31.43 ± 1.17 a20.19 ± 0.87 c14.89 ± 0.47 e
pH6.56 ± 0.02 a6.24 ± 0.02 cd6.23 ± 0.02 d6.23 ± 0.03 d6.25 ± 0.03 bcd6.28 ± 0.02 b6.27 ± 0.02 bc
Lactic acid (%)0.21 ± 0.02 c0.37 ± 0.01 a0.38 ± 0.02 a0.37 ± 0.01 a0.33 ± 0.01 b0.33 ± 0.01 b0.32 ± 0.01 b
Total solids (%)35.09 ± 0.16 e35.14 ± 0.14 e36.20 ± 0.19 c36.70 ± 0.10 a35.34 ± 0.12 d36.65 ± 0.15 ab36.50 ± 0.17 b
Fat (%)5.82 ± 0.26 a5.98 ± 0.27 a5.92 ± 0.22 a5.85 ± 0.16 a5.92 ± 0.22 a5.97 ± 0.20 a5.95 ± 0.20 a
Mean (n = 6) ± standard deviation. Different letters in the same row indicate significant differences among the ice creams (Duncan’s test, p < 0.05). C = control, Y = ice cream with yoghurt culture, Y-WF = ice cream with yoghurt culture and wheat fibre, Y-INU = ice cream with yoghurt culture and inulin, LR = ice cream with L. rhamnosus, LR-WF = ice cream with L. rhamnosus and wheat fibre, LR-INU = ice cream with L. rhamnosus and inulin.
Table
Table 5. Physical and chemical properties of the yoghurt and probiotic ice creams on the first day of the storage.
Table 5. Physical and chemical properties of the yoghurt and probiotic ice creams on the first day of the storage.
PropertiesCYY-WFY-INULRLR-WFLR-INU
Tm (°C)1.88 ± 0.96 a0.79 ± 0.11 bc−1.15 ± 0.27 e0.45 ± 0.31 bcd1.20 ± 0.35 ab−0.09 ± 0.50 d0.00 ± 0.05 cd
Tg (°C)−28.65 ± 1.59 a−28.61 ± 1.04 a−30.72 ± 1.75 a−28.31 ± 1.70 a−28.72 ± 1.04 a−29.68 ± 1.17 a−30.09 ± 0.95 a
Mean (n = 3) ± standard deviation. Different letters in the same row indicate significant differences among the ice creams (Duncan’s test, p < 0.05). Tm: Melting temperature, Tg: Glass transition temperature, C = control, Y = ice cream with yoghurt culture, Y-WF = ice cream with yoghurt culture and wheat fibre, Y-INU = ice cream with yoghurt culture and inulin, LR = ice cream with L. rhamnosus, LR-WF = ice cream with L. rhamnosus and wheat fibre, LR-INU = ice cream with L. rhamnosus and inulin.
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Sezer, E.; Ayar, A.; Yılmaz, S.Ö. Fermentation of Dietary Fibre-Added Milk with Yoghurt Bacteria and L. rhamnosus and Use in Ice Cream Production. Fermentation 2023, 9, 3. https://doi.org/10.3390/fermentation9010003

AMA Style

Sezer E, Ayar A, Yılmaz SÖ. Fermentation of Dietary Fibre-Added Milk with Yoghurt Bacteria and L. rhamnosus and Use in Ice Cream Production. Fermentation. 2023; 9(1):3. https://doi.org/10.3390/fermentation9010003

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Sezer, Elif, Ahmet Ayar, and Suzan Öztürk Yılmaz. 2023. "Fermentation of Dietary Fibre-Added Milk with Yoghurt Bacteria and L. rhamnosus and Use in Ice Cream Production" Fermentation 9, no. 1: 3. https://doi.org/10.3390/fermentation9010003

APA Style

Sezer, E., Ayar, A., & Yılmaz, S. Ö. (2023). Fermentation of Dietary Fibre-Added Milk with Yoghurt Bacteria and L. rhamnosus and Use in Ice Cream Production. Fermentation, 9(1), 3. https://doi.org/10.3390/fermentation9010003

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