Physical and Sensory Evaluation of Peanut Yogurt

The word “yogurt” is related to the Turkish word “jaukurt” which means thick milk. Yogurt refers to a fermented milk product made by using selected microorganisms to develop not only the characteristic flavor but also body and texture. Peanut is one of the important nutrients which has significant amount of all essential nutrients. Objective: In this study physical and sensory properties of peanut yogurt are evaluated by using different scientifically proved sensory evaluation methods.  Methods: Organoleptic evaluation of yogurt showed that storage as well as treatments had significant effect on all sensory parameters and a progressive deterioration in flavor, body & texture and appearance of yogurt under various preparatory treatments. Results: Among treatments, highest scores were awarded to treatment containing 10 % peanut milk, 80 % skimmed milk liquid, 9 % skimmed milk powder and 1 % sugar, for all parameters and minimum changes were noted in it during the whole period of study. Recent investigation revealed that treatment T1 (10 % peanut milk) was comparatively best for manufacturing of peanut milk yogurt followed by T2 (20 % peanut milk + 70 % skimmed milk liquid + 9 % skimmed milk powder + 1 % sugar) while peanut milk yogurt from (30 % peanut milk + 60 % skimmed milk liquid + 9 % skimmed milk powder + 1 % sugar) had the lowest degree of firmness and organoleptic acceptance. Conclusion: It was noticed that correlation among fat, total solids and protein contents in peanut milk affect the extent of serum separation and pH of yogurt and ultimately the texture and overall acceptability of yogurt.

In most countries yogurt is popular cultured dairy product all the time. On the subject of possible health bene ts of yo g u r t , t h i s i s to s o m e ex te n t d u e to a b e t te r responsiveness of customers. Yogurt is enriched with protein, fat, phosphorus, calcium etc. which has a high nutritional value, easily digestible, and its role in total phosphorus intake has been reported as 33-44 %. During fermentation, yogurt is milk based product which can digest quickly due to presence of milk protein, lactose and fat components undertake fractional hydrolysis [1].
Between various milk products manufactured through fermentation, that may include butter milk, acidophilus milk, sour cream, ropy milk, and cheese owing, yogurt is possibly the most popular one because of its refreshing aroma, avor, and creamy consistency [2]. Fermented foods offer a wide range of texture, avor and aroma to improve the value of human diet. More than 3500 fermented foods are distributed all over the world [3]. For production of peanut milk yogurt mostly research has been done on utilization of fermentation techniques for and protein content has higher rmness or viscosity. Viscosity also affects the mouth feel and texture of uid [12]. The sensory properties can be adversely affected by various possibilities, among them is an increased number of stabilizers which can change avor and make the overall texture over-stabilized, giving a gel-like mouthfeel. While comparing peanut yogurt, it can be produced without the need of added solids or stabilizers having solids content of 16-18 % in the milk [13]. The consistency and brittleness level of yogurt could be achieved by changing fat and protein levels. Protein component was used most effectively to enhance consistency. The yogurt having large protein components (7.39 %) created less number of pores and have lower syneresis as compared to lower protein yogurts [14]. The forti cation of the peanut milk for manufacturing of yogurt milk was done by 4g/100g skimmed milk powder and 12g/100g total solids. These were later subjected for physiochemical assessment by leveraging CMY as control for the study. When compared to CMY peanut milk yogurt has higher content of protein, water holding capacity [15], fats and unsaturated fatty acids also higher than saturated ones [16].

M E T H O D S
extraction of peanut milk in the presence of lactic acid bacteria. Moreover, the presence of extensive nutty and whey avor may turn the whole thing into an unsuitable product for yogurt substitution [4]. Peanut has an important role in ghting against malnutrition due to its phytochemical and nutrient content [5]. A yogurt-like product (Dahi) was pro tably produced using lactic cultures with miltone (derived by supplementing spraydried peanut protein isolates with animal milk). Although, the fermentation in the involvement of L. acidophilus NRRL B-1910 and L. bulgaricus NRRL B-1909 develops a custard like texture in peanut milk but extreme amount of whey can make the product unpleasant. The ever-changing norms of consumers for natural products owes to the developing comprehension on human health ailment because of synthetic additives. In food systems different types of additives are in use i.e. coloring agents, avoring agents and variety of preservatives. Antioxidants play a major role in scavenging free radicals for the mitigation of oxidation processes, marking them as important additives as compared to others [6]. Despite of the inferior quality of peanut milk yogurt as compare to that of yogurt from cow milk it is consumable and had good textural properties and its overall acceptability scores were also satisfactory. In yogurt production, S. thermophilus and L. bulgaricusas starter cultures are required for fermentation. Due to this reason, for development of proper color and avor, interaction between starter cultures and their individual characteristics are of much importance [7]. According to the main characters i.e. texture is the only one which de nes the yogurt quality [8]. -examined the effects of several attributes and ingredients on the preference and sensory perception of the yogurt. It was noted that acidity played an important role in aroma and avor of the yogurt as compared to acetaldehydes like 2,3-pentanedione and diacetyle [9]. -observed the physical characteristics and shelf-life of yogurt made of corn milk. They compared physico-chemical, microbiological characteristics and shelf-life of corn milk and cow milk yogurt (CMY). Results of this study recommend that corn milk is a prospective raw material for making an innovative yogurt. The corn milk yogurt had low fat contents [10], protein with harder and higher consistency than CMY. The physical appearance, color and avor of corn milk yogurt and commercial yogurt were not much different. The main avor compounds of CMY were tridecane, tetradecane, dodecane and heptyl methyl ketone whereas those of corn milk yogurt were tridecane, ethyl oleate, tetradecane, ethyl linoleate [11]. Viscosity or rmness plays an important role in determining the quality and acceptability of the yogurt without syneresis. The rmness of the yogurt is affected by the source of milk and the yogurt with higher total solids Procurement of raw materials: Peanuts, raw milk, skimmed milk, sugar and chemicals (Lactobacillus bulgaricus and Streptococcus thermophilus) are the materials that were used for this study. All these materials were purchased from the local market with a care that all the materials should be of good quality. Peanut milk yogurt was manufactured and analyzed in the Laboratory of National Institute of Food Science & Technology, University of Agriculture, Faisalabad. Preparation of peanut milk: Firstly, peanuts were washed and soaked in water for seven hours at room temperature. Then peanuts were grounded followed by water which was twice of peanut weight. Peanut milk was obtained by ltering the resultant slurry through centrifugal separator with a double layered cheese cloth. It was heated for 15 min at 90 °C. Physical and sensory properties were determined by following methods. Yogurt syneresis was evaluated from the centrifugation process, conducted with a couple of alterations. The liberation of watery-whey like liquid on the surface of the gel is termed as syneresis. 200g of yogurt sample (Y) was taken and prepared inside a centrifuge cup which was then subjected to centrifugation for 10 minutes at 2500 RMP with an average 640xg at 4°C. The weight of the expelled whey content (W) was analyzed and then eliminated while the syneresis was examined by the following formula; [17] Apparent viscosity of yogurt was determined at 10 to 15ºC and the obtained yogurt was then agitated for more than 40 R E S U L T S seconds prior to measuring the overall viscosity. With a rotation of around 10 RPM, spindle 4 was utilized for the previously described measurement. Two units of reading were used, a) percent torque and b) centipoises (cP) for taking the Viscometer reading. Yogurt samples were evaluated for color, avor, body/texture and overall acceptability using 9-point hedonic scale by the panel of researchers from the faculty members at the National Institute of Food Science and Technology, University of Agriculture, Faisalabad [18]. The data obtained for each parameter was subjected to statistical analysis under factorial design using completely randomized design (CRD). Interaction was carried out up-to two ways. Statistix 8.1 software was used to analyze data statistically according to the method described by [19]. seconds prior to measuring the overall viscosity. With a rotation of around 10 RPM, spindle 4 was utilized for the previously described measurement. Two units of reading were used, a) percent torque and b) centipoises (cP) for taking the Viscometer reading. Yogurt samples were evaluated for color, avor, body/texture and overall acceptability using 9-point hedonic scale by the panel of researchers from the faculty members at the National Institute of Food Science and Technology, University of Agriculture, Faisalabad [18]. The data obtained for each parameter was subjected to statistical analysis under factorial design using completely randomized design (CRD). Interaction was carried out up-to two ways. Statistix 8.1 software was used to analyze data statistically according to the method described by [19].     The results regarding the viscosity of peanut milk yogurt under various treatments during storage exposed that viscosity decreased in peanut milk yogurt through entire period of storage due to increase of shear rate. The peptide chains of peanut milk proteins are unfolded with high temperatures, which may cause the change in the nature of the protein and viscosity altered [20]. The apparent viscosity of yogurt was extremely affected by the content of total solids of yogurt, it was observed that with an increase in the total solids there was a change in apparent viscosity [2]. The viscosity or rmness of peanut milk yogurt samples under various treatments decreased during storage. At zero day the highest rmness/viscosity values were observed (267.33 cP) in yogurt sample T1 of 10% peanut milk and minimum value (251.33cP) was observed in yogurt sample T3 of 30% peanut milk. After 15 days of storage minimum decrease in viscosity value (8.66) was observed in peanut milk yogurt sample T2 of 20% peanut milk. Changes in viscosity were graphically showed in g1.
The statistical analysis showed that the change in viscosity was highly signi cant for treatments as well as storage and their interaction was non-signi cant. The main defect of yogurt which should be overcome during storage is the whey separation. The syneresis of yogurt under various treatments increased due to increase in acidity during storage. The increase in syneresis might be due to rearrangement of protein network resulting from changes in pH, acidity and temperature during storage of yogurt.
The results regarding the syneresis of yogurt under various treatments during storage are shown in g 2, which showed that syneresis increased in yogurt through storage period. The increase in syneresis values after 15 days of storage were from40.54 to 45.87, 38.93 to 44.75, 40.33to 46.93and 42.47 to 47.99for 0% peanut milk to 30% peanut milk respectively. The statistical analysis demonstrated that the results were highly signi cant for treatments, storage days and their interaction during storage. All samples of prepared peanut milk yogurt were organoleptically evaluated at 0, 5, 10 and 15days intervals using 9-point hedonic scale. Five judges were provided with printed Performa. The data collected on organoleptic evaluation i.e. avor, body, texture and appearance was associated with quality and the acceptability of cultured dairy products as affected by storage are discussed below. Color and Appearance: The data on the appearance of peanut milk yogurt under various treatments during storage is given in Table1. The mean score for appearance decreased like other characteristics during storage. The mean score for appearance after 15 days' storage decreased from 8.37 to 6.75 for T0, 7.92 to 6.93 for T1, 6.84 to 5.76 for T2 and 6.39 to 5.31 for T3 respectively. The data in Table 4.19 showed that there was maximum decrease in the scores for appearance T1 while T2 got maximum score. The appearance of yogurt is also affected due to increase in yeast and mold counts in yogurt during storage, which ultimately deteriorates the quality of yogurt. Flavor is a combined perception of taste, smell and mouth feel [21]. When it is requested to give comments on the avor of the two yogurts, some judges cherished the PMY avor upon that of CMY but the most judges favored the CMY avor. These indications recommend that if we improve the avor of PMY, then PMY turn out to be more satisfactory and appealing to prospective customers. The data on avor scores of yogurts under various treatments as affected by storage is shown in Organoleptic evaluation of yogurt showed that storage as well as treatments administered major impact on all sensory parameters and a progressive deterioration in avor, body & texture and appearance of yogurt under various preparatory treatments and storage time. [3] [4]