1 Introduction

Dairy products, especially fermented products such as labneh are the main and most popular vehicles of probiotics due to their compatibility with probiotic microorganisms, pleasant sensory profile, and high consumption around the world [1]. Labneh, yoghurt cheese, strained yoghurt or Greek yoghurt is a yoghurt which has been strained in a cloth bag, then packaged and stored in refrigerator for consumption and this known with the traditional method [2, 3] or it is made using ultrafiltration process (UF) to remove the whey or permeate, respectively giving a consistency between that of yoghurt and cheese and had little sour taste [2]. However, both traditional process and UF technique are the two main methods used for the manufacture of labneh in the most of dairy plants. The total solids of Labneh about 22–26%, which is suitable for consumption [3].

Imbalanced diet can cause many diseases; therefore, functional foods that can adjust the body function and prevent lifestyle diseases of civilization have attracted more attention in recent years [4, 5]. Also, Dietary fiber has outstanding health promotion functions, some plants contain high dietary fibers such as Oats (Avena sativa L.) [4]. The multifunctional benefits and nutritional composition of Oats makes it popular; because it is a good source of dietary fiber minerals and other nutrients. It is also a good source of B complex vitamins, protein and fat. The β-glucan in Oats has outstanding functional properties and is of immense importance in human nutrition and helpful against coeliac disease. Many bioactive compounds were found in Oats; these compounds possess antioxidant activity.

Oats also has promoting immunomodulation as it can prevent diseases and some forms of cancer. Furthermore, Oats help in the treatment of diabetes and cardiovascular disorders and lowering cholesterol. The incorporation of Oat grains in the food products improves not only the nutrition but also a therapy against many maladies, so, Oats can act as one of the most promising functional foods of the future [6, 7]. Therefore, the objective of this work is: (i) Supplementation of the buffaloes’ milk retentate with different ratios of Oats powder as prebiotic and using probiotic bacteria for making functional synbiotic UF-low and full-fat Labneh, comparing with that made by traditional method (ii) Studying the effect of adding different ratios of Oats on the viability of the probiotic bacteria, nutritional value, fiber content, some chemical, and sensory properties of resulted Labneh.

2 Materials and methods

Fresh raw buffaloes’ milk was obtained from the farm of Fac. Agric., Fayoum Univ., Egypt. Partially Skimmed ultra-filtrated (UF) buffalo's milk retentate was obtained from dairy plant of General Authority Agrarian Reform, Ministry Agric., Fayoum, Egypt. Full fat UF-buffalo's milk was obtained from dairy processing pilot plant, Fac. Agric., Fayoum Univ., Egypt. The strains of lactic acid bacteria (LAB) used in this study as probiotic culture is L. casei (HQ177095) and L. paracasei (HQ177096.1) (LAB). These strains were previously isolated and identified by Elbanna et al. [8, 9], Khider and Elbanna [10]. Also, direct vat starter (DVS) containing Str. thermophiles and L. bulgaricus (YCX11) was obtained from Chr. Hansen's laboratories, Denmark. The isolates of LAB were activated first in MRS broth medium, then activated in 10% (w/v) sterilized skim milk at 37 °C for 24 h under microaerophilic conditions. Santé oat flakes (Avena sativa L.) made of whole grain Oats (produced by Santé Company, Poland) was obtained from local markets. Ultra-pure salt (NaCl) produced by the Egyptian salts and minerals company (EMISAL) was used. All chemicals and reagents that used for this study were analytical grade and obtained from Sigma, Merck, El-Nasser and El-Gomhouria Companies.

3 Methods

3.1 Preparation of Oats powder

Oat flakes (7% fat, 66% carbohydrates, 11% fibers, 17% protein and 26% iron, according to the chemical composition of the manufacturer package) was grinded using the grinder of electrical blender and kept in powder form till use in clean plastic bags to avoid moisture absorption.

3.2 Preparation of traditional and functional UF-Labneh

Full and low-fat labneh were made from fresh buffaloes' milk (16.30% total solids (TS), 5.7% fat, 5.20% protein, 4.56% lactose and pH 6.6) and low-fat buffaloes' milk (standardized to 2% fat) as described by Tamime and Robinson [11]. The full and Low-fat functional Labneh and control was made as described in Fig. 1. Ultrafiltration process for fresh full-fat buffaloes' milk was done to get final concentration of 35% TS and 10% fat, similarly low-fat fresh buffaloes' milk was ultrafiltrated to final concentration of 30% TS and 5% fat. Both resulted UF-retantates (concentrated to factor 2.5×) were used to make functional UF-Labneh according to the method described by Shamsia and El-Ghannam [12]. The added starter (2%), was a mixture of both L. casei and L. paracasei (1:1) and the treatments were made as shown in Fig. 1. The treatments of supplemented Labneh and control was made as follow:

  • C1: Low fat Labneh made with traditional method

  • C2: Full fat Labneh made with traditional method

  • L1: UF-law fat Labneh (free of Oats) + probiotic bacteria (L. casei and L. paracasei (1:1)

  • L2: UF-law fat Labneh (1% of Oats powder) + probiotic bacteria (L. casei and L. paracasei (1:1)

  • L3: UF-law fat Labneh (2% of Oats powder) + probiotic bacteria (L. casei and L. paracasei (1:1)

  • L4: UF-full fat Labneh (free of Oats) + probiotic bacteria (L. casei and L. paracasei (1:1)

  • L5: UF-full fat Labneh (1% of Oats powder) + probiotic bacteria (L. casei and L. paracasei (1:1) and

  • L6: UF-full fat Labneh (2% of Oats powder) + probiotic bacteria (L. casei and L. paracasei (1:1).

Fig. 1
figure 1

Schematic flow diagram of the basic steps involved in Labneh made by traditional method and ultrafiltration technique with supplementation of Oats powder

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Samples of both controls and all supplemented Labneh treatments, were analyzed for chemical composition (Total solids, fat, protein, lactose and ash) at fresh age and at the end of cold storage (5 °C ± 1) period (21 and 35 days for both controls and supplemented treatments, respectively). Also, nutritional value were calculated and determined in all fresh samples, while, pH values, titratable acidity (TA%), microbiological and sensory attributes were determined during 35 days of storage at 5 ± 1 °C.

3.3 Chemical analysis

Raw milk and Labneh samples were analyzed for their total solids (oven drying method), titratable acidity (expressed as lactic acid), fat (Gerber method), total protein contents (macro Kjeldahal method) calculated by multiplying nitrogen percent by 6.38, lactose content (phenol sulphoric method), total dietary fibers and total ash, as described in AOAC [13]. The pH values of the samples of each treatment were determined by using pH meter (Thermo Scientific Orion Star, A214).

3.4 Nutritional value

The energy content of experimental Labneh calculated as described by FAO [14]. The daily values (%DV) are based on the daily values for key nutrients which is calculated using Food and Drug Administration list of %DVs based on a caloric intake of 2000 kcal, for adults and children aged 4 years and older [15].

3.5 Microbiological examination of Labneh

Media used in this study (MRS agar, MacConkey agar, PCA and PDA) were prepared as described in Oxoid [16].

3.6 Organoleptic properties

The organoleptic properties of functional Labneh samples were evaluated by 10 panels of staff members of Dairy Sci. Depart., and Food Sci. and Technol. Depart., Fac. Agric., Fayoum Univ. Labneh samples were evaluated according to the score card sheet of Amer et al. [17] intervals storage period: fresh, 7, 15 and 21 days. The total score (100 points) was divided into 50 points for flavor, 40 points for body and texture and 10 points for appearance.

3.7 Statistical analysis

The results were statistically analyzed using General Linear Model’s procedure of Statistical Package for Social Sciences [18] Version 17.0.0 software. Duncan’s [19] multiple range tests were used to compare between the means.

4 Results and discussion

4.1 Approximate composition of Labneh supplemented with Oats

4.1.1 Total solids and fat content

In this study approximate composition including total solids (TS), fat, protein, ash, lactose, lactose hydrolysis rate, pH values and total acidity (TA%) were determined in Labneh treatments.

Results in Table 1, illustrate the effect of using UF-technique and adding different ratios of Oats powder to low and full-fat Labneh on its total solids and fat content, comparing with control made with traditional method. Regarding total solids content, there is a significant difference (P ≤ 0.001) among different treatments and control. In general, all samples of Labneh increased in its TS content during the cold storage period, which may due to moisture loss [20, 21]. It is worth mention that Labneh contain Oats has the highest TS content and it increased with increasing the added levels from Oats. The highest values were, 27.54 and 27.60% for L6 treatment when fresh and at 35 days old, respectively, this increase in TS relate to the added amount of Oats powder, which contain high fiber affect the final total solids [7]. While, the lowest values were in control (C1), as it recorded 22.07 and 22.19% at same previous ages, respectively. Similar results for labneh free of Oats were obtained by Thabet et al. [22] but not agreement with Elkot et al. [23], as they mentioned that the total solids in Labneh free of additives was 29.51%. All values of TS in Labneh treatments were in accordance to the Egyptian Standard range, where all low-fat Labneh treatments had TS content > 22% whereas, full fat treatments had TS content > 26% according to the Egyptian standards [24]. Labneh samples made by UF-technique had the highest TS content either when fresh or at the end of storage (35 days) compared with that made by traditional method; similar trend was obtained by EL-Ahwal et al. [21].

Table 1 Total solids, fat, protein and ash contents of low and full-fat Labneh as affected by adding different ratios of Oats powder and storage periods at 5 °C ± 1
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Regarding the fat content of low and full-fat Labneh (Table 1), there was no much change in fat content in all treatments during storage. There is a significant difference (P ≤ 0.05) in fat content among all treatments and both controls, but not significant between UF-low fat treatments or between UF-full fat treatments. Depending on the type of treatment, fat content of all fresh UF-low fat labneh treatments (L1, L2 and L3) were more than that in fresh traditional low-fat labneh (C1), where it was 5.00 and 4.00%, respectively. Similarly, in fresh UF-full fat Labneh treatments (L4, L5 and L6) have the same fat reading (10.50%), it was higher than fresh traditional full fat labneh (C2) which recorded 10% fat. The low fat content in control made by traditional method; may be due to fat loss with whey through the cloth bag during its manufacture [25]. Results of TS and fat content are in agreement with findings of El-Shafei et al. [26] and Thabet et al. [22]. Moreover, all labneh treatments were corresponding to the Egyptian standards [24].

4.1.2 Protein and ash contents

Protein and ash contents in samples of all Labneh treatments show no high significant differences and controls during storage period (Table 1). The total protein content was slightly increased at the end of the storage period in all treatments. Total protein of all low fat Labneh treatments (C1, L1, L2 and L3) was higher than that in full fat treatments (C2, L4, L5 and L6). Also, it's observed that as the concentration of Oats increased, the protein content of Labneh samples increased due to its high protein content [7]. These results explained that L6 treatment (full fat UF-labneh supplemented with 2% Oats), after 35 days had the highest protein content of 12.43%. While, fresh low fat labneh (C1) made by traditional method recorded the lowest protein value of 8.87%, which may relate to penetration and loss of some whey proteins and some other protein derivatives from the cloth bag during traditional Labneh drainage [25].

Similarly, ash content shows little increase at the end of the storage period in all samples of Labneh treatments. The highest ash content (2.81%) was recorded in low-fat labneh that supplemented with 2% Oats (L3) at 35 days of storage. On the other hand, the lowest ash reading (1.76%) was recorded in fresh samples of full fat labneh (C2) made by traditional method, which close to the finding of Elkot et al. [23]. In general, these results are in agreement with those of Ozer et al. [27], Zayan et al. [28], Thabet et al. [22] and Atamian et al. [29]; they gained similar ranges of TS, protein and fat in both UF-labneh and traditional labneh.

4.1.3 Lactose content and rate of its hydrolysis

Lactose content decreasing in labneh is an indication to increasing the rate of its hydrolysis. There are some wide variations in lactose content among the treatments and between control and treatments (Fig. 2a). Samples of fresh low fat traditional labneh (C1) had the significantly (P ≤ 0.05) higher lactose content; of 5.03% than samples of the other treatments during storage. While, the lowest lactose contents were for treatments which contained 2% Oats either UF-low fat (L3) or UF-full fat labneh (L6) at 35 days of storage as it was 3.70 and 3.60%, respectively. These results are in accordance with the results reported by Zayan et al. [28], El-Shafei et al. [26] and Hassabo [3]. On the other hand, the highest rates of lactose hydrolysis (Fig. 2b); were, 9.75 and 8.39% for treatments, L3 and L6 at 35 days, respectively. This could be attributed to the high ratio of Oats in these treatments; which play an important role as it activates the probiotic bacteria (Lactobacillus casei and paracasei) which further hydrolyzed lactose [30]. Also, Basiony et al. [2] reported that Labneh supplemented with Oats recorded high viable count of lactic acid bacteria and as a result it hydrolyzed lactose to lactic acid. On the other hand, it is observed that the rate of lactose hydrolysis is higher in low-fat Labneh treatments than full-fat Labneh treatments, this may relate to the little inhibition effect occurred by milk fat on the growth of LAB in low-fat Labneh treatments.

Fig. 2
figure 2

Changes in lactose content (a), rate of lactose hydrolysis (b), pH values (c) and titratable acidity (d) of both controls (C1, C2), low and full-fat Labneh supplemented with different ratios of Oats powder during storage at 5 °C ± 1

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4.1.4 Changing in pH values and titratable acidity

Changes occurred in the pH values and total acidity (TA%) of various Labneh samples of the different treatments during storage are presented in Fig. 2c, d, respectively. The results revealed that there are no much differences between treatments, little decrease in the pH values of all Labneh samples along the cold storage period was noticed. The pH values (Fig. 2c) of all fresh Labneh samples ranged from 4.51 to 4.60. It is also observed that the lowest pH values at 21 days of storage period were, 3.90 and 3.96 for both Labneh control samples; C1 and C2 made by traditional method, respectively. In addition, pH values of all low fat treatments (C1, L1, L2 and L3) were less than values of full fat Labneh samples (C2, L4, L5 and L6). These results were in harmony with study made by El-Shafei et al. [26] and El-Gazzar et al. [31], who reported that fresh Labneh had pH value ranged from 4.6 to 4.8, it is clear from the results that the pH decreased during storage period in all samples, and this also in agreement with what reported by Nsabimana [32].

The TA% (Fig. 2d) of all Labneh treatments increased significantly (P ≤ 0.05) during storage period, it ranged between 0.90 and 1.10% in fresh samples. It's also observed that the highest TA% were noticed at 21 days of storage for low-fat and full-fat traditional Labneh; C1 and C2, respectively, where both achieved 2.25%, followed by UF-low fat Labneh supplemented with 2% Oats (L3), which recorded 2.17% at 35 days of storage. The results revealed that TA% was increased in the resultant UF-Labneh treatments as the added level of Oats powder was increased. Such increase is attributed to lactose hydrolysis and production of lactic acid by LAB. The same trend was reported by Zayan et al. [28] and Basiony et al. [2] and close to what obtained by Thabet et al. [22] and EL-Ahwal et al. [21].

4.1.5 Nutritional value of experimental Labneh

Results of nutritional value and percent daily value (%DV) of experimental Labneh are presented in Table 2. Every value of each component is calculated in proportion to the daily needs. Energy refers to the total number of calories supplied from all sources (fat, carbohydrate, protein) in one serving of the food. To achieve or maintain a healthy body weight, balance the number of calories you eat and drink with the number of calories you burn during physical activity and through your body’s metabolic processes. In general, 100 cal per serving is moderate while 400 cal per serving is high [15]. Results indicated that all low-fat and full-fat Labneh treatments are moderate in calories. The lowest number was for traditional low-fat Labneh (C1); of 98.52 cal whereas; the highest energy was 156.46 cal for the full-fat UF-Labneh supplemented with 2% Oats powder (L6).

Table 2 Nutritional and percent daily values (%DV) of nutrients in low and full-fat Labneh as affected by adding different ratios of Oats powder
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Daily Value percent (%DV) shows how much a nutrient in a single serving of the food or dietary supplement contributes to your daily diet. The %DVs are based on the Daily Values for key nutrients, which are the amounts (in grams, milligrams, or micrograms) of nutrients recommended per day for humans 4 years of age and older. Also, %DV is used to compare food products and to choose products that are higher in nutrients you want to get more of and lower in nutrients you need to get less. As a general rule, 5% DV or less of a nutrient per serving is low, while, 20% DV or more of a nutrient per serving is high. Moreover, FDA issued a list of DVs based on a caloric intake of 2000 cal, for adults and children four or more years of age [15, 33].

The results indicated that all low-fat Labneh treatments provide human by high protein amount daily (20% DV or more) where L3 recorded the highest % DV of protein (24.52%). While, the lowest % DV of protein was recorded for traditionally full-fat Labneh (C2) of 17.74%. Moreover, full-fat Labneh treatments are considered a good source of fats as it provides adults with about 12.82–13.46% of their daily needs from fats. On the other hand, all treatments were low in total carbohydrates and fibers and it is less than the DV. The lowest %DV of carbohydrate was 1.49%, which recorded for samples of both C2 and L4 Labneh treatment. On the other hand, the highest % DV values of carbohydrates were 2.04 and 2.01%, which recorded for samples of L3 and L6 Labneh treatments, respectively. It may due to supplementing Labneh with 2% Oats which contains about 80% total carbohydrates [34], also they reviewed that whole grain oat contains 10–11% dietary fibers. It explains that both L3 and L6 (low-fat and full-fat UF-Labneh contain 2% Oats) recorded higher %DV (0.86%) of dietary fibers than other treatments, while C1, C2, L1 and L4 Labneh treatments; that made without Oats, were free of dietary fibers. Generally, it is recommended taking different sources of food to obtain the needs from fiber and carbohydrates.

4.2 Microbiological examination of experimental Labneh

4.2.1 Viability of probiotics bacteria

The starter used in traditional Labneh making was L. bulgaricus and Str. thermophilus (1:1). Whereas, the probiotic starter used in making functional UF-Labneh treatments was L. casei and L. paracasei (1:1). In this study LAB count was increased in Labneh treatments that supplemented with Oats more than control and other treatments made without Oat. The results in Fig. 3a, illustrated that the interaction between treatments and storage period significantly (P ≤ 0.001) affected counts of LAB. The treatment L3 at the 35 days of storage recorded the highest number of LAB (208.66 × 108 CFU/g), while, Fresh C2 had the lowest count of LAB (14.33 × 108 CFU/g). The obtained results have the same trend of the findings of Basiony et al. [2], they showed a decrease in the number of LAB (yogurt culture) of the functional Labneh supplemented with different functional ingredients after 10 days of storage, and they reported that Labneh supplemented with Oats had higher counts of LAB than that supplemented with wheat germ, top of sugar cane and barley. Oats are good source of non-digestible carbohydrates that besides promoting several beneficial physiological effects can act as prebiotics that selectively stimulate the growth of Lactobacilli. These results were in accordance with that gained by Reid [30]. Also, Oats contains beta-glucan which is postulated to improve probiotic survival in dairy products during cold storage [35]. Full-fat and low-fat controls samples made by traditional method (C1 and C2, respectively) were spoiled after 21 days of storage while, all UF-Labneh treatments were valid till 35 days. So, microbiological counts hadn't been determined in traditional controls at 28 and 35 days of storage period.

Fig. 3
figure 3

Changes in the viability of Lactic acid bacteria (a), total viable counts (b), fungi (c) and psychrophilic bacteria (d) (CFU/g) of both controls (C1, C2), low and full-fat Labneh as affected by adding different ratios of Oats powder during storage at 5 °C ± 1

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4.2.2 Total viable count, fungi, psychrophilic bacteria and coliform counts

Results in Fig. 3b, show the effect of treatments and storage period on TVC of Labneh. The interaction between treatments and storage period significantly (P ≤ 0.001) affected TVC where, the treatment L3 at the 35th day had the highest TVC (131.00 × 108 CFU/g). This is in agreement with Saad et al. [36], they represented that TVC increased gradually in Labneh during storage. Also, results are in accordance with Basiony et al. [2], they reported that oat's Labneh treatments had higher TVC than control and other cereals.

Fresh samples of treatments L4, L5 and L6 had significantly (P ≤ 0.001) lower TVC; 16.66 × 108, 17.33 × 108 and 19.66 × 108 CFU/g, respectively than other treatments at different storage periods. These results of low TVC might be due to great inhibitory effect of the probiotic L. casei and L. paracasei against spoilage and pathogenic bacteria; which leads to limiting its growth as reported by Shokryazdan et al. [37], where UF-Labneh treatments had lower TVC numbers than Labneh which made by the traditional method (C1 and C2).

The fungi count among the Labneh samples of different treatments during the storage period was shown in Fig. 3c. Both traditionally low and full fat Labneh (C1 and C2) had a short shelf life as it spoiled after 21 days of storage, whereas, C2 Labneh recorded the highest fungal count of 64.00 × 102 CFU/g, followed by C1 Labneh as the observed count was 59.66 × 102 CFU/g. All Labneh samples made by UF-technique or with added Oats powder, were free from fungi at fresh age and was little count at 21 days of storage. These results are in agreement with what reported by Yang and Clausen [38], Hassan and Bullerman [39], they found that L. casei and L. paracasei were able to inhibit growth of yeasts and moulds. In addition, LAB and their antimicrobial metabolites have potential bio preservative effect to control the growth of spoilage and pathogenic bacteria in foods [40].

Regarding psychrophilic bacteria, the results of interaction between treatment and storage period (Fig. 3d) indicted that low-fat traditional Labneh (C1) stored for 21 days had the significantly highest psychrophilic bacteria counts of 348.00 × 102 CFU/g (P ≤ 0.05). While, fresh control full fat UF-Labneh (L4) had lower counts than other treatments during storage (13.66 × 102 CFU/g). In general, due to the lower pH value (4.2–4.6), fermented milks is not a suitable environment for the majority of spoilage-causing bacteria [41]. The negative impacts of psychrophilic bacteria on the quality of milk and dairy products are unquestionable. Their ubiquitous nature in the production environment and ability for rapid growth under low temperatures have made this group of bacteria the leading direct and/or indirect cause of spoilage of milk and dairy products. Contamination of raw milk with psychrophilic bacteria, even under the best manufacturing practices, cannot be completely avoided [42].

All Labneh treatments were free from coliform bacteria either when fresh or during storage periods at 5 °C ± 1. These results might be due to the strong effect of heat treatment, the probiotic starter on coliform bacteria and also, the sanitation and hygienic conditions during the manufacture process of Labneh. This finding is conformable to that obtained by Thabet et al. [22].

4.2.3 Organoleptic properties of experimental Labneh

Results presented in Fig. 4, showed the effect of the interaction between treatment and storage period on organoleptic properties of Labneh. It is significantly affected flavor (Fig. 4a) and total score but, there were insignificantly effect on appearance (Fig. 4b) or body and texture (Fig. 4c) of Labneh. Low fat UF-Labneh (L1) stored for 7 days and the low fat UF-Labneh supplemented with 1% Oats (L2) stored for 28 days had higher total score (Fig. 4d) of 97.60 and 97.40 points, respectively but it insignificantly differs from all other UF treatments. However, the traditional low fat control treatment (C1) stored for 21 days gained lower total score of 70.20 points. Both, C1 and C2 (low-fat and full-fat traditional labneh) had a short shelf life as it had been spoiled after 21 days of storage. There were insignificant differences found among all treatments regarding body and texture and appearance for organoleptic properties of Labneh that ranged between 39.00 and 31.40 points for body and texture and ranged between 9.80 and 7.20 points for appearance. These results are in accordance with what reported by Ali [43] and Basiony et al. [2] as they mention that using Oats for supplementation of some dairy products such as Labneh, ice cream and yogurt, gain overall acceptability.

Fig. 4
figure 4

Scores of sensory evaluation for both controls (C1, C2), low and full-fat Labneh as affected by adding different ratios of Oats powder and storage periods at 5 °C ± 1, flavor (a), body and texture (b), appearance (c) and total scores (d)

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5 Conclusion

In this study using UF-technique and adding Oats powder in making Labneh, improved the nutritional value as it increased protein, %DV and fiber contents and decreasing lactose content and that suitable for people who suffer from lactose intolerance. Also using the probiotic bacteria which produce bacteriocins; minimize the fungi and psychrophilic bacterial counts comparing with control. Moreover, addition of Oats powder increased the viability of the probiotic bacteria and improve the flavor especially the treatments made with 1% Oat comparing to the control.