Background: probiotic yogurt fortified with pistachio-pellet. Materials

Background:Theimprovement of structural characteristicsof low-fat functional dairy products has always been of great importance. Thepurpose of the present study was to evaluate the physicochemical properties oflow-fat probiotic yogurt fortified with pistachio-pellet.Materialsand Methods: Kalle-Ghuchi pistachio kernel residue(pellet) was prepared after extracting the oil through cold-pressing. Probioticstarter (ABT-10) was then added to low-fat milk and the sample was divided intothree portions (T1-T3).

T1 was the control. T2 and T3 were treated with 2% and4% pistachio-pellet, respectively. After incubation at 42°C, the products werekept at 4°C for 14 days. During this period, the products’ physicochemicalproperties were investigated. The results were analyzed using a one-way ANOVA(P<0.05).Results: Adirect relationship was observed between the amount of pellet and the productacidity. Additionally, spontaneous syneresis reduction was detected during thisperiod.

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Water holding capacity (WHC) of the fortified portions of yogurt wasnot affected by pellet treatment. Regarding yogurt color changes, lightness (L*)reduction, greenness (a*), and yellowness (b*) enhancement wereobserved compared to the control portion.Conclusions:Enrichingyogurt with the proteins of pistachio pellet not only improves the physicalstructure of low-fat yogurt gel but may also enhance its functional properties,including bioactivity and being satisfactory for cardiovascular health.

 Keywords:pistachio;pellet; yogurt; physicochemical properties  1.                  IntroductionIran is one of the countries wherepistachio (Pistacia Vera L.) is cultivated. In addition to having micro-and macro-nutrients, pistachio kernels have significant nutritional value andare used as food ingredients due to the presence of various antioxidantclasses, such as anthocyanins, tocopherols, carotenoids, chlorophylls,flavonoids, isoflavones, proanthocyanidins, anacardic acids, cardanols,resveratrol, and vitamin C (1-3).The amount of kernel oil varies indifferent types of pistachios, and, in some cases, it exceeds 75%.

This oil ismainly used in food and cosmetics industry. Using the cold-press technique inpistachio kernel oil extraction reduces the amount of antioxidant destructionand also causes minimum organoleptic changes in the product (2). It has been shown that the amount of totalantioxidant activity (TAA) of pistachio hydrophilic extract, as a source ofpolyphenols, is higher than its lipophilic extract (4, 5). After the extraction of pistachio oil, the remainder containssignificant amounts of protein, fiber, and micronutrients, which can be used inmany industries, including the food industry. Nowadays, functional foods are widelyused to improve people’s well-being and health (6).Products containing probiotic bacteria are examples of these functional foodsthat have several health benefits (7). Therefore,maintenance and improvement of physicochemical and functional properties ofprobiotic products are of great importance for the palatability, consumption,and marketability of these products.The purpose of the present study was toinvestigate the physicochemical properties of protein-enriched probiotic yogurtby adding the nutritious pistachio residues, obtained after the extraction ofkernel oil, in order to produce a nourishing functional product.

 2.                  Materialsand methods2.1.             Pistachio preparationThe pistachios(Kalle-Ghuchi cultivar) were purchased from a local supermarket in the city ofKerman, Iran. In order to determine the physical properties of the nuts andtheir kernels, 50 individual nuts/kernels were randomly selected. The pistachionut and the kernel were weighed using a scale and the three principaldimensions length, width, and height were measured using a Vernier caliper (with an accuracy of 0.02mm).

The length (L), width (W), and height (H) of pistachio nut and also thedimensions of pistachio kernel (i.e. length (l); width (w) and height (h)),were measured, as shown in Fig. 1 (8-10). 2.2.

             Pistachio-pellet preparationInorder to prepare the pistachio-pellet, the oil was extracted using a screwpress (Iran Cold Press®, Model 85 mm express, Iran). The pistachio kernels wereintroduced directly into the press while the tip of the press had previously beenheated to ensure proper oil extraction. The oil temperature was controlled not toexceed 45°C. After oil extraction, the produced pistachio-pellets were storedat -18°C in dark glass bottles to avoid oxidation until the analysis and usage stages(11). 2.

3.             Chemical analysis of yogurt ingredientsTodetermine the moisture content and the dry matter, milled pistachio kernels andtheir pellets were heated using an oven at 103±2°Cuntil a constant weight was reached (8, 9).Dried samples were also analyzed for total ether-extractable fats using a Soxhlet extractor, and thetotal proteins were determined through the standard micro-Kjeldahl method in atleast triplicate. The proteins were calculated by the protein factor of 6.25.Milk protein (micro-Kjeldahl), fat (Gerber method), and moisture content (ovenmethod) were also determined (12-14).

 2.4.             YogurtpreparationThe whole yogurt preparation procedurewas performed in a hygienic condition. The homogenized and pasteurized milk washeated up to 85°C for 30 min, followed by cooling down to 42°C. The probioticyogurt starter culture ABT-10 (Chr.

Hansen®, Denmark) containing Lactobacillusacidophilus La-5 and Bifidobacterium animalis subsp. lactis BB-12® wasthen added at a concentration of 0.05% w/v to the milk. The cultured milk wasdivided into three equal portions (T1, T2, and T3). The dry matter of T2 and T3were increased by 2% and 4% with pistachio-pellet fine powder, respectively,while T1 received nothing (the control group).

All the 3 groups were separatelypoured into 250-mL plastic cups and incubated at 42°C until their pH decreasedto 4.6. The cups were then stored at 4±1°C for 14 days and the physiochemicaltests were performed at 1, 7, and 14 days of storage. The experiments wereperformed triplicate. 2.5.

             pHdeterminationA Selecta pH meter 2001 (J.P. Selecta,Spain) was used to determine the pH of the yogurt samples on the above-mentioneddays at room temperature (15). 2.6.             Titratableacidity (TA)Ten grams of each yogurt samples werediluted with distilled water (2-fold) and titrated with NaOH (0.1 M) in thepresence of phenolphthalein.

The TA of a single cup of yogurt per replicationwas expressed as the percent of lactic acid (v/w) (15). 2.7.

             ColorparametersColor parameters L? (lightness: 100representing white and 0 representing black), a? (redness-greenness:positive representing red and negative representing green), and b? (yellowness-blueness:positive representing yellow and negative representing blue) were measuredusing a digital imaging modified method described by Yam and Papadakis (2004)with a slight modification. Photos of the samples were captured using a Canondigital camera (PowerShot SX20 IS, 12.1 megapixels, Japan) installed in asituation described by Abbasvali et al. (2012). The images were analyzed 4times per sample in the lab mode to obtain L?,a?, and b? color values usingPhotoshop version 11.0. Color values were then averaged to obtain a mean valuefor each yogurt cup per replication (16, 17). 2.

8.         Spontaneous syneresisThe siphon method was used to determinethe amount of spontaneous whey separation in the set-yogurt (18). After being taken from the cold room (4°C), a cup of yogurt was immediately weighed and tilted at an angle of 45° forwhey collection using a syringe.

The cup of yogurt was weighed again. Toprevent further outflow of whey from the set yogurt, the siphoning was repeatedwithin 10 s. The spontaneous syneresis (%) was expressed as follows (Eq. 1):                        Eq. 1 2.9.

         Susceptibility to syneresis (STS)Determination of STS was evaluated usingthe drainage method with some modifications (15,18, 19). Approximately 50 g of the set yogurt was cut in a single actionby a ladle. The gel was then weighed and drained on a sieve (an aperture of 38?m) for 15 min at room temperature.

Susceptibility to syneresis (%) wascalculated using the following formula (Eq. 2):                                                                             Eq.2 2.

10.          Water-holding capacity (WHC)The yogurt samples were stirred 25 timesclockwise and anticlockwise with a glass rod to measure their WHC utilizing thecentrifugation method (Universal 320 R, Hettich Zentrifugen, Germany) withseveral modifications (18). Thirty gramsof yogurt were centrifuged at 3313×g for 15 min at 10°C, and the WHC wascalculated as follows (Eq. 3):                                                          Eq.3 2.11.

          Statistical analysisThe obtained data were represented asmean±standard deviation (SD) and werethen analyzed using IBM SPSS Statistics version 19.0. Differences inbetween-subjects variables wereconsidered significant at p<0.05 using a one-way ANOVA, followed bythe Duncan's post-hoc test. 3.             ResultsThe appropriate kernel: nut weight ratioin Kalle-Ghuchi cultivarand the size of its dimensions are among the important physical factors formarketing of this product (Table 1).The extraction of pistachio oil by meansof screw cold-pressing reduced the amount of sample oil by 62.9%.

This oilreduction was accompanied by an increase in the pellet protein percentage from9.35% to 27.70%.

Furthermore, this oil extraction decreased the indices ofpellet lightness (L*), greenness (a*), and yellowness (b*)values in comparison to the kernel (Table 2).Enrichment of the yogurt with the pistachio-pelletdecreased the pH value compared to the control group during the first 7 days.Notably, the increase in the acidity of the fortified yogurt was observed notonly regarding the plain yogurt but also with an increment in the amount ofadded pellet (from T3 to T2) over a period of 14 days (Table 3).On day 1, the spontaneous syneresisrate, which was measured immediately after taking the yogurt from the cold room(4°C), did not differ among the different groups, while susceptibility tosyneresis of the control group at room temperature and after 15 minutes ofdraining was higher than the enriched yogurt samples.

Spontaneous syneresis ofthe enriched samples was significantly lower than the control group after 7 and14 days. On day 14, the reduction of spontaneous syneresis was even moreevident when comparing fortified yogurt with the control group (plain yogurt),and even the T3 samples showed a lower amount of syneresis than the T2 samples(1.37% versus 2.

25%) (Table 3).Plain yogurt samples (the control group)had less lightness than the milk (Tables 2 and 4). Although there was not anydifference in the lightness of fortified yogurt samples on the first day, after7 and 14 days, enriched yogurts started to show less lightness (Table 4).

Thecolor parameter “a*” indicated an increase in the greenness of theyogurt samples containing pistachio-pellet compared to the control yogurtwithin 14 days. The Increase in the yogurt yellowness in comparison with theinitial milk is clear in the control group (Tables 2 and 4). The higher amountof b* value in the enriched yogurt samples in comparison with thecontrol group indicates higher yellowness of these fortified products. Notably,after 7 and 14 days, the differences in yellowness were observed not only incomparison with the control group but also in T3 and T4 (Table 4). 4.             DiscussionThe presence of significant amounts of proteinand calcium in pistachio and its pellets makes it an appropriate candidate forthe enrichment of food, especially dairy products.

In addition, the presence ofsubstantial amounts of fiber in pistachio-pellet is likely to increase its usein products containing beneficial bacteria, including probiotics (2).So far, pistachio protein, which mainlycontains globulin (66%), albumin (25%), glutelin (7.3%), and prolamin (2%), hasbeen used in the preparation of edible films (20,21). In this study, the protein content of pistachio kernel was measuredat 9.35%, which was similar to the findings of Hayoglu and Gamli (3).

The pistachio-pellet application as asource of protein and carbohydrate in yogurt production increased thetitratable acidity of dairy products compared to the control group, such thatafter 14 days the produced lactic acid in T2 and T3 samples reached 1.41% and1.59% levels, respectively (Table 3).

This could be due to the role ofpistachio-pellet nutrients as a prebiotic and to the increase in the milk solidcontent to improve the activity of lactic acid bacteria of the yogurt samples (22). In addition, pistachio nut paste has beenshown to be slightly acidic, and at 20°C its pH declines to 5.61 after 7 monthsof storage (23).The syneresis is defined as the breakingdown of protein gel network and the separation of its serum phase (24).

The amount of whey separation from yogurtis evaluated in a variety of methods. Spontaneous syneresis measures the wheyseparation on the surface of set yogurt gel, while the drainage method (STS)brings about the rate of whey leakage from its cutting surface (18). In this study, the 2% increase in thedry matter of milk by pistachio-pellet reduced the spontaneous whey separationof yogurt by 26.38%, 50.89%, and 64.

11%, during the days 1, 7, and 14,respectively. The decrease in spontaneous syneresis of T4 groups, in which theamount of dry matter increased by 4%, was 37.72%, 26.

72%, and 70.07%,respectively, on the same days (Table 3). It has been shown that increasing thetotal solid content can play an important role in reducing the whey isolation (25-27).

Although some use high levels of milkfat in order to reduce yogurt syneresis, adding pistachio-pellet not onlyenriches yogurt in terms of protein but also enhances its antioxidant content (28). In this study, increased acidity did nothave a stimulating effect on the spontaneous syneresis of the enriched samples(Table 3). Since susceptibility to syneresis forgels like cottage cheese is more informative than yogurt, there was nosignificant difference in drainage rate between the control group and theenriched yogurt samples except for the first day (18). The amount of whey isolated in the centrifuge method (WHC) isalso influenced by other factors, such as the rheological properties and theproduct rigidity, and, in this study, no significant difference was found amongthe groups (Table 3).The decrease in the enriched yogurtslightness on days 7 and 14 is due to the addition of pistachio-pellet, when itslightness was 22 times less than the pistachio kernel.

Pistachio and its pelletare green in color due to their chlorophyll content. Finally, the increase in theyellowness (b*) and also the greenness (a*) indices is due to thepresence of pistachio pigments in the fortified yogurts. 5.             ConclusionsLow-fat yogurts have an important rolein cardiovascular-friendly diets due to a reduced fat content. Since thepresence of fat has an important effect on a product’s texture and theimprovement of its physical and technological properties, the marketability andpalatability of the products are affected by fat reduction.

There are several strategies,including using gum, to improve this condition. After extracting pistachiokernel oil, the residual pellet has a high protein and fiber content. The aboveproperties, as well as the presence of antioxidant compounds in the pellet,make it an ideal candidate for the preparation of yogurt as a dairy productwith a protein matrix. In this study, pistachio-enriched yogurt, which has ahigh nutritional value, has shown favorable physicochemical characteristics,especially in terms of spontaneous syneresis reduction and also syneresissusceptibility which, accordingly, could provide a suitable place in people’sdiet. 


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