This study examined the quality of some yoghurts made and sold in the Nigerian market. Nine

commercially available brands of yoghurt drinks which represent seven different manufacturers were

randomly selected. The samples included seven plain yoghurt and two fruit yoghurt samples. All yoghurt

samples were analyzed for chemical properties (moisture%, ash %, total solids, SNF, fat, pH and titratable

acidity) and the organoleptic tests (color, thickness, appearance, body, texture, taste, smell, flavor and over

all acceptability). The results of the study showed that the physico-chemical composition of the manufactured

yogurts was different. The pH values of the samples ranged between 3.70-4.33 which were reasonably

suitable for yoghurt marketed in tropical areas. No direct relationship was observed between pH values and

titratable acidity. There was marked variation in the % fat content of the products. The results of the sensory

evaluation revealed that flavor with respect to taste and smell had significant influence (p<0.05) on overall

acceptability of yogurt product. So, the yogurt manufacturers need to improve on the sensory properties in

particular flavor and taste for better consumer acceptability. Also, they may improve on packaging by labeling

to specifications that precisely represent the content and type

OLUGBUYIRO, J.A.O

English

Covenant University Repository

Pakistan Journal of Nutrition 10 (10): 914-918, 2011ISSN 1680-5194© Asian Network for Scientific Information, 2011Corresponding Author: Joseph A.O. Olugbuyiro, Department of Chemistry, College of Science and Technology, Covenant University,Ota, Ogun State, Nigeria914Physico-chemical and Sensory Evaluation of Market Yoghurt in NigeriaJoseph A.O. Olugbuyiro and Joy E. OsehDepartment of Chemistry, College of Science and Technology, Covenant University, Ota, Ogun State, NigeriaAbstract: This study examined the quality of some yoghurts made and sold in the Nigerian market. Ninecommercially available brands of yoghurt drinks which represent seven different manufacturers wererandomly selected. The samples included seven plain yoghurt and two fruit yoghurt samples. All yoghurtsamples were analyzed for chemical properties (moisture%, ash %, total solids, SNF, fat, pH and titratableacidity) and the organoleptic tests (color, thickness, appearance, body, texture, taste, smell, flavor and overall acceptability). The results of the study showed that the physico-chemical composition of the manufacturedyogurts was different. The pH values of the samples ranged between 3.70-4.33 which were reasonablysuitable for yoghurt marketed in tropical areas. No direct relationship was observed between pH values andtitratable acidity. There was marked variation in the % fat content of the products. The results of the sensoryevaluation revealed that flavor with respect to taste and smell had significant influence (p<0.05) on overallacceptability of yogurt product. So, the yogurt manufacturers need to improve on the sensory properties inparticular flavor and taste for better consumer acceptability. Also, they may improve on packaging by labelingto specifications that precisely represent the content and type.Key words: Yogurt, chemical evaluation, sensory properties, consumer acceptanceINTRODUCTIONYoghurt is a fermented milk product and consumed bylarge segments of our population either as a part of dietor as a refreshing beverage. It is a nutritiously balancedfood containing almost all the nutrients present in milkbut in a more assimilable form. It is obtained by lacticacid fermentation of milk through the action of a starterculture containing Streptococcus thermophilus andLactobacillus bulgaricus. (Adolfsson et al., 2004). Yoghurt samples: Nine commercially available brandsHuman consumption of yoghurt has been associated of yoghurt drinks in the Nigerian market were randomlywith tremendous health benefits due to improvement of selected (Table 1). The samples were registered bygastrointestinal functions and disease risk reduction National Agency for Food and Drug Administration and(Heyman, 2000). Control (NAFDAC) at the time of this study. The trade andDifferent forms of yoghurt are available in the market like manufacturers’ names, ingredients and packagingsweetened or flavored, stirred, strained, set, frozen and methods of the yoghurt products were obtained from theliquid yoghurt. The consumption of yoghurt in Nigeria labels on the products and recorded. Samples werehas increased during the last decade and is taken as evaluated by a random experiment with 3 repetitions fordessert or refreshing beverage drink. The quality of each sample and the mean of the three values wasyoghurt in local market varies from one producer to recorded.another. Poor quality milk, unhygienic practicesassociated with the process involved and the use of pH measurement: The pH was determined at room“wild type” of starter culture give rise to poor grade temperature (27 C) using a digital pH meter (JENWAY(Younus et al., 2002) However, the inclusion of non-diary 3505). The pH meter was calibrated with bufferingredients have been found to improve yogurt quality, standards of pH 4 and pH 10 prior to use. 50 ml of eachcreate new brands of yogurts and modulate perception yoghurt drink was placed in a beaker, the probe of theof consumers (Karagul-Yuceer et al., 1999; Iwalokun pH meter was inserted and pH value was recorded. Thisand Shitu, 2007). It is therefore important to carry out an measurement was done on opening of the yoghurt. Theinvestigation on the characteristics of the yogurt sold in probe was rinsed thoroughly with distilled water beforelocal markets to ascertain their quality in relation to used on sample.consumer preference. Therefore, this present studyevaluated some types of yoghurt in the Nigerian marketfor chemical and organoleptic properties with the view ofassessing the quality of the yoghurt with reference tostandards and to determine the consumer acceptanceof such product. MATERIALS AND METHODSoTitre value x M x 90 x 100Titratable acidityVolume of sample x 1000=(Weight of dish Dry yoghurt)(Weight of dish)Total solids (%) x 100Weight of the sample+−=Pak. J. Nutr., 10 (10): 914-918, 2011915Table 1: Commercial yoghurt drinks investigatedSample Trade name Manufacturer Ingredient Packaging1 Holandia Strawberry CHI Limited, Nigeria Yoghurt base, sugar, strawberry concentrate, Tetra packYoghurt (HS) stabilizer (E440),  water, colour (E124)2 Holianda pineapple/coconut CHI Limited, Nigeria Yoghurt base, sugar, pineapple concentrate, Tetra packYoghurt (HC) coconut juice, natural pineapple, coconutflavor, stabilizer and water3 Mr Cream Yoghurt (MC) TOB-TECH Enterprises, Full cream milk powder, sugar, vanilla PlasticNigeria flavor, treated water and yoghurt culture4 De Thirsty Yoghurt (DT) Thirsty Drink NIG. ENT. Milk, sugar, yoghurt culture, water and flavor Plastic5 Finest Yoghurt (FN) Finest Foods, Chemicals Water, skimmed milk, sucrose and Plasticand Allied product LTD. stabilizer6 Splenda Yoghurt (SP) Slenda Food Water, sugar, milk, yoghurt culture and flavor Plastic7 Holianda plain Sweetened CHI Limited, Nigeria Yoghurt base, sugar, stabilizer, water Tetra packYoghurt (HP)8 Superyogo (SY ) Fan milk PLC Milk solid not-fat, starter culture, sugar, Sachetvegetable fat, stabilizer  (E1422, E471,E401, E412)9 Cedar Yoghurt (CD) Cedar ‘D’ Vine LTD. Milk, calcium, protein, vitamins, minerals, Plasticcarbohydrate, essential fatty acidsTitratable acidity: The titratable acidity was measured by Fat determination: The fat content was determined bytitrating 15 ml of the yoghurt with 0.1 M sodium hydroxideuntil the substance reached a pH value 8.2,corresponding to the end point of the phenolphthalein.Readings were done with pH meter (JENWAY 3505).When this value was reached, the spent NaOH volumewas recorded and the acid percentage of the substancewas calculated using the formula: Where, M = Molar concentration of NaOHMoisture content determination: The moisture contentof the yogurt products was determined according to theAssociation of Official Analytical Chemists method(AOAC, 1995). Each yoghurt product (10 g) was placedin an oven at 105 C for 3 h. Reading was taken at aoconstant weight. The moisture content was thenexpressed as the percentage (%) of the dry weight ofsample.Total solids: The weight of the residue obtained frommoisture content analysis was expressed aspercentage total solids using the formula below:Ash content determination: The ash content of each ofdry yoghurt samples was determined at 550 Coaccording to AOAC (1995). The ash content is expressedas the inorganic residue left as a percentage of the totalweight of yoghurt incinerated.the modified Mojonnier ether extraction method (AOAC,1995). The extracted fat is dried to a constant weight andexpressed as percent fat per weight.Solids-not-fat: Solids-not-fat was determined byconducting total solids and fat analyses. Percent fat wassubtracted from percent total solids to obtain percentsolids-not-fat.Sensory evaluation: All the samples were evaluated fororganoleptic characteristics and overall acceptability by15 panelists that comprised undergraduate, graduatestudents, teaching and non-teaching staff members ofCovenant University, Ota, Nigeria; using nine pointhedonic scale ranging from excellent (score = 9) to verypoor (score = 0) as extremes (Obi et al., 2010).Statistical analysis: The data obtained were computedas mean±standard deviation and analyzed by Analysisof Variance (ANOVA). RESULTS AND DISCUSSIONIngredient and packaging of yogurt products: Table 1shows the trade names, ingredients, manufacturers andpackaging of the nine yoghurt samples. Two (HS andHC) of the products were fruit stirred yoghurts while theremaining seven (MC, DT, FN, SP, HP, SY and CD) wereplain yoghurts. All the products contained two or moreadditives such as sucrose, flavor, color and stabilizer.Three of the products (HS, HC and HP) were enclosedin tetra pack; one in sachet (SY) and the remaining five(MC, DT, FN, SP and CD) were packed in plasticcontainers.pH: The pH of the yogurt samples are summarized inTable 2. Sample DT showed the highest average pH ofPak. J. Nutr., 10 (10): 914-918, 2011916Table 2: pH and Titratable acidity (Mean±SD) of the yoghurt Table 3: Chemical composition of yoghurt samples in percent samplesSample pH SD Titratable acidity (%) SD Sample content content solids content not-fat1. HS 4.11 0.01 0.30 0.03 HS 79.1 0.26 20.9 2.75 18.152. HC 4.10 0.02 0.36 0.02 HC 80.0 0.26 20.0 2.07 17.933. MC 4.08 0.02 0.50 0.07 MC 78.2 0.71 21.8 3.03 18.774. DT 4.33 0.02 0.22 0.04 DT 87.1 0.31 12.9 3.41 9.495. FN 3.85 0.01 0.43 0.04 FN 86.8 0.40 13.2 3.18 10.026. SP 3.81 0.01 0.50 0.05 SP 83.5 0.36 16.5 4.00 12.507. HP 4.06 0.03 0.31 0.03 HP 82.9 0.38 17.1 2.04 15.068. SY 4.00 0.01 0.33 0.06 SY 80.8 0.31 19.2 2.05 17.159. CD 3.70 0.03 0.39 0.04 CD 86.3 0.33 13.7 1.88 11.824.33 with standard deviation of 0.02 while CD shows the Fat content: The fat content of the yoghurt samples arelowest average pH of 3.70 standard deviation of 0.03. shown in Table 3. There was variation in the percent fatWith the exception of DT, the plain yogurts were more content. The highest average fat content is 4.00% whileacidic with mean pH range from 4.08-3.70 as against the lowest average fat content is 1.88%. According to4.11-4.10 of lactic acid content for fruit yoghurt. The USDA (2001), yoghurt with less than 0.5% fat contentvariation in the pH of DT (4.33) when compared with should be labeled as” not fat yoghurt”, those with fatother samples could be due to its composition during content  within  the  range  of  0.5-2.0%  before  theproduction. The pH values observed in this study are addition of bulky should be labeled “low fat yoghurt” andcomparable to other workers (Dublin-Green and Ibe, those with fat content above 3.25% should be labeled“2005; Hassan and Amjad, 2010). All the same, the pH yoghurt.results are in accordance with FDA specifications for thepH of yoghurt (4.6 or lower). Solids-not-fat: The SNF of the yoghurt samples areThe pH values of the samples were reasonably justified shown in Table 2. The average range is from 9.49-and suitable for yoghurt marketed in tropical areas 18.77% According to USDA specification (2001) and FDAbecause of the expected effect of bad storage conditions (2009), yoghurt should contain not less than 8.25% SNFsuch as high temperatures encountering in some zones before the addition of bulky flavour the present findingsin Nigeria which can affect the acidity of yoghurt. conform to this specification.Titratable acidity: The titratable acidity of the yoghurt is Sensory properties: Table 4 displays the observedshown in Table 2. Samples MC and SP had the highest attributes of the yogurts with reference to USDAtitratable acidity of 0.50 while sample DT had the lowest specifications (2001) whereas the mean scores fortitratable acidity of 0.22. The values obtained for titratable sensory evaluation of sample yoghurts are shown inacidity are generally below the standard which is 0.7% Table 5. Sample 1 (Table 4) had a clean pink color while(FDA,  2009).  No direct relationship was observed all other samples presented natural color ranging frombetween pH values and titratable acidity as has been bright white to off-white color. There is no significantpreviously reported (Dublin-Green and Ibe, 2005). difference (p>0.05) in the mean color scores (Table 5).Moisture content and Ash content: As shown in Table color distribution of the test products. 3, the moisture content of the samples ranged from The appearance of samples 3, 5, 6 and 9 (Table 4)78.2-87.1%. MC  had the least percent of moisture lacked velvety feeling and were not fully homogenous incontent this justified its thickness which the panelists texture compared to others this is in agreement withaveragely rated very thick. The values obtained for ash their mean appearance scores (4.2, 5.1, 4.4 and 4.3content of the yoghurt samples had a range between respectively) which were below average (5.7).0.26-0.71%. The mean scores for thickness had a range of 4.3 to 7.7Total solids content: The total solids content of each exhibited good custard-like body; their mean thicknesssample is shown in Table 3. Sample MC had the scores (7.7 and 7.5) are significantly different from otherhighest total solids of 21.8% this value supported its products (p<0.05). Samples 4, 6 and 9 were evaluatedfirm, custard-like body (table). Apart from MC, the two fruit thick liquids while the remaining products 1, 2 7 and 8yoghurts contained more total solids (20.9% and 20.0%) had no significant difference in mean scores (p>0.05)than plain yoghurts which ranged from 12.9-19.2%. and rated low in thickness compared to others (Table 5)Dublin-Green and Ibe (2005) reported values for fruit and in conjunction with Table 4 they are simply liquid yogurts.natural yoghurts ranging from 15.0-22.8% and 13.6- Karagul-Yuceer et al. (1999) stated that some yogurts18.8% respectively these were in close range with our exhibit a heavy consistency that closely resemblesfindings. custard  or  milk  pudding. In  contrast, other  yogurts  areMoisture Ash Total Fat SolidsThe results demonstrated that there was uniformity in(Table 5) on a 9-point scale. In Table 4, items 3 and 5Pak. J. Nutr., 10 (10): 914-918, 2011917Table 4: Sensory characteristics of the yogurtsSensory quality--------------------------------------------------------------------------------------------------------------------------------------------------------------Sample Color App/texture Body Taste Smell1 Pink Smooth Watery Sweet with sour Pleasant2 Natural Smooth Watery Sweet Pleasant3 Natural Rough Firm Sweet with sour Pleasant4 Natural Smooth Thick Sour Fair5 Natural Fairly smooth Firm Sour Unpleasant6 Natural Wheyey Thick Harsh Fair7 Natural Smooth Watery Sweet with sour Pleasant8 Natural Smooth Watery Sweet with sour Pleasant9 Natural Rough Thick Sweet with sour PleasantTable 5: Mean scores of sensory properties and overall acceptability of the yogurtsSensory property--------------------------------------------------------------------------------------------------------------------------------------------------------------------------Sample Color App Thickness Flavor Taste Smell O.A1 6.5  (0.3) 6.9  (0.4) 4.4  (0.3) 7.2  (0.3) 6.9  (0.3) 7.0  (0.3) 7.1  (0.2)a a a a a a a2 6.6  (0.2) 7.0  (0.3) 4.4  (0.3) 6.1  (0.4) 6.0 (0.3) 6.2  (0.4) 6.7  (0.2)a a a b b b a3 6.8  (0.3) 4.2  (0.3) 7.7  (0.2) 5.7  (0.4) 5.8  (0.4) 5.3  (0.4) 5.9  (0.4)a b b b b c b4 6.5  (0.2) 6.0  (0.4) 6.3  (0.2) 4.7  (0.3) 4.3  (0.2) 4.9  (0.4) 4.3  (0.3)a c c c c c c5 6.4  (0.3) 5.1  (0.4) 7.5  (0.3) 2.9  (0.4) 4.5  (0.4) 3.1  (0.5) 2.6  (0.4)a c b d c d d6 6.5  (0.3) 4.4  (0.4) 6.4  (0.3) 4.5  (0.4) 2.6  (0.3) 5.1  (0.4) 3.0  (0.3)a b c c d c d7 6.9  (0.3) 6.4  (0.4) 4.3  (0.3) 6.0  (0.3) 7.0  (0.4) 6.2  (0.3) 6.9  (0.3)a c a b a b a8 6.8  (0.3) 6.4  (0.3) 4.4  (0.3) 6.8  (0.3) 6.9  (0.4) 6.9  (0.4) 6.8  (0.3)a c a a a a a9 6.5  (0.2) 4.3  (0.3) 6.5  (0.2) 6.5  (0.3) 6.7  (0.3) 6.3  (0.4) 6.5  (0.2)a b c b a b a1-9 = Yoghurt samples, App = Appearance, OA = Overall acceptability, Figures in parentheses represent. SEM of the mean values ofdata. Means within a column without a common superscript differ (p<0.05)purposely soft-bodied and are essentially drinkable. The acceptability of each product. The three products (4, 5differences observed in product thickness agree with and 6) that were significantly scored low (p<0.05) inthat statement. overall acceptability showed a direct relationship withTable 4 shows that samples 1, 3, 7, 8 and 9 had their mean scores for flavor, taste and smell.sweetness with clean acid taste undertone. Product 2possessed plain sweet taste in contrast with samples Conclusion: The results of this research showed that4 and 5 which had sharp sour taste. However, sample 6 though consumer might have preference for variation inpossessed unpleasant taste with reference to other yogurt consistencies, a pleasant flavor coupled with aproducts. Products 1, 2, 3, 7, 8 and 9 scored (Table 5) perceptible sensation of product sweetness hadhigher than the average mean scores for flavor and taste significant influence on overall acceptability of the(5.7 and 5.6 respectively). The mean flavor and taste product. So, the yogurt manufacturers need to improvescores for samples 4, 5 and 6 (Table 5) are significantly on the sensory properties in particular flavor and tastebelow average (p<0.05). The results from the two tables for better consumer acceptability. Also, they may improveof sensory properties in conjunction with pH values on packaging by labeling to specifications that precisely(Table 2)  indicate  that  a  perceptible  sensation  of represent the content and type.product sweetness coupled with a pleasant taste ofacidity is more preferred to ordinary acid taste yoghurt.Sample  5  had  no flavor and the smell was unpleasantto consumer. The means scores (2.9 and 3.1respectively) are significantly very low (p<0.05)compared to other products which averagely displayedpleasant smell. Although color, appearance, texture and thickness ofyogurt are important quality characteristics, the flavor ofthe product is generally considered the most critical andimportant indicator of consumer acceptance (Bodyfelt etal., 1988). Results (Table 5) of the consumeracceptance evaluation showed that flavor with respect totaste and smell had over whelming influence in overallREFERENCESAdolfsson, O., S.N. Meydani and R.M. Russel, 2004.Yogurt and gut function. Am. J. Clin. Nutr., 80: 245-256.AOAC, 1995. Official Methods of Analysis of theAssociation of Official Analytical Chemists. Vol II16th ed.,AOAC Arlington, VA.Bodyfelt, F.W., J. Tobias and G.M. Trout, 1988. SensoryEvaluation of Dairy Products. Van RostrandReinhold, New York.Dublin-Green, M. and S.N. Ibe, 2005. Quality evaluationof yogurts produced commercially in Lagos, Nigeria.Afr. J. Applied Zool. Environ. Biol., 7: 78-82. Pak. J. Nutr., 10 (10): 914-918, 2011918FDA, 2009. Milk and cream products and yogurt Karagul-Yuceer, Y., P.C. Coggins, J.C. Wilson and C.H.products. Food and Drug Administration Federal White, 1999. Carbonated yogurt-sensory propertiesRegister, 74: 2448. and consumer acceptance. J. Dairy Sci., 82: 1394-Hassan Ammara and Amjad Imran, 2010. Nutritional 1398.evaluation of yoghurt prepared by different starter Obi, T.E., F.O. Henshaw and O.O. Atanda, 2010. Qualitycultures and their physiochemical analysis during evaluation of plain-stirred probiotic yoghurtstorage. Afr. J. Biotech., 9: 2913-2917. produced from skim and whole milk powder duringHeyman, M., 2000. Effect of lactic acid bacteria on refrigerated strorage. EJEAFChe, 9: 1203-1213.diarrheal diseases. J. Am. Coll. Nutr., 19: 137S- USDA, 2001. Specifications for Yogurt, Nonfat Yogurt146S. and Lowfat Yogurt. Document 21CFR, Part 131.200-Iwalokun, B.A. and M.O. Shitu, 2007. Effect of hibiscus 203.Sabdariffa (Calyce) extract on biochemical and Younus, S., T. Masud and T. Aziz, 2002. Qualityorganoleptic properties of yogurt. Pak. J. Nutr., 6: evaluation of market yoghurt/Dahi. Pak. J. Nutr., 1:172-182. 226-230.

Physico-chemical and Sensory Evaluation of Market Yoghurt in Nigeria

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Physico-chemical and Sensory Evaluation of Market Yoghurt in Nigeria

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