ABSTRACT
There is an increasing trend in yoghurt consumption due to the health benefits from the gut bacteria present in yoghurt. However, there is need to evaluate other inexpensive nutrient sources such as spices (turmeric) which contain a lot of phytochemicals to make yoghurt more nutritious. Fresh turmeric rhizome was sorted, washed, peeled and milled. Ethanol was added to obtain turmeric extract. The turmeric extract was added to the yoghurt before (YTBF) and after fermentation (YTAF) at different ratios of yoghurt: Turmeric (95:5, 90:10, 85:15, 80:20, 75:25 and 100:0). Proximate composition and sensory characteristics of the blends were determined using standard procedures. Results obtained show that the addition of turmeric extract to the yoghurt had significant (p < 0.05) effect on the parameters analyzed. The protein, fat, ash and carbohydrate content of YTBF samples ranged from 2.70 - 3.98, 1.56 - 1.74, 0.20 - 0.38 and 7.69 - 8.25%, respectively while that of sampled YTAF ranged from 2.64 - 3.85, 1.53 - 1.69, 0.24 - 0.54 and 7.87 - 8.26%, respectively. From the sensory scores, sample with the lowest level of turmeric extract (YTBF1) (95:5) was most preferred and compared favorably with the control sample based on colour, taste and overall acceptability. The incorporation of turmeric extract in yoghurt improved the nutrient content of the yoghurt samples. Increased levels above 10% (90:10) led to a more intense colour and spicy taste which did not appeal to the panelists.
Key words: Yoghurt, turmeric, fermentation, proximate composition, sensory characteristics.
Yoghurt is a product of the lactic acid fermentation of milk by addition of a starter culture containing Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus. In some countries, less traditional microorganismms such as Lactobacillus helveticus and Lactobacillus delbrueckii ssp. lactis, are sometimes mixed with the starter culture (McKinley, 2005).Yoghurt is valued for controlling the growth of bacteria and in curing of intestinal disease such as constipation, diarrhoea and dysentery, anti-carcinogenic effect and lowering of blood cholesterol (Kamruzzaman et al., 2002). Due to the aforementioned health benefits, there is an increasing trend for yoghurt consumption and is the fastest growing dairy sector in the market, in particular, standard yoghurt and yogurt drinks. Yoghurts come in a variety of textures (e.g. liquid, set and stirred curd), fat contents (e.g. regular fat, low-fat and fat-free) and flavours (e.g. natural, fruit, cereal, chocolate), and can be consumed as a snack or part of a meal, as a sweet or savoury food.
Yoghurt is generally considered as a safer product and its unique flavour, is so appealing that consideration is being given by nutritionists to incorporate inexpensive source of nutrients in order to make it an almost complete food (Boghra and Mathur, 2000). Nowadays, yoghurts are being sold with different flavours. For instance, ginger and herbs are added to the fresh milk before fermentation or served with sugar syrup. Various fruits, vegetables and spices e.g. turmeric are being incorporated into yoghurts to give them desirable flavours. Turmeric (
Curcuma longa L.) is a rhizomatous herbaceous perennial plant of the ginger family (Zingiberaceae) originated in tropical South Asia but is now widely cultivated in the tropical and sub-tropical regions of the world (Jurenka, 2009).It has a warm, bitter taste and is frequently used to flavour or colour curry powders, mustards, butters, and cheeses. It contains a yellow-coloured chemical substance called curcumin, which is often used to colour foods and
cosmetics (Akande and Adegoke, 2018).
Curcumin is the main active ingredient in turmeric responsible for turmeric's numerous activities. It is known to possess anti-oxidative (Cousins et al., 2007), anti- microbial (Cho et al., 2006) and anti-inflammatory properties as well as having radio-resistant and chemo-preventive properties (Bar-sela et al., 2010).
Yoghurt is naturally produced from milk which contains a reasonable amount of live cultures mainly bacteria. Milk, from which yoghurt is made, contains a reasonable quantity of fat globules referred to as milkfat. Yoghurt therefore is prone to oxidation and can produce off-flavor. However, there are some spices that possess anti-oxidative, anti-microbial and anti-inflammatory properties which if incorporated in yoghurt, can help avert the off-flavour. However, it is most likely that the main reason that spices are being used is because, they help keep the foods free of unwanted microorganisms and thus contribute to health (Brul and Coote, 1999). However, spices such as turmeric are known to contain proteases and to have proteolytic activity (Nagarathnam et al., 2010).
Therefore, a yoghurt product with spice extract should serve to provide the combined health benefits from the spice plus those from the gut healthy bacteria present in the yoghurt. The objective of this study was to produce stirred yoghurt with graded levels of turmeric and evaluate the effect of turmeric in the yoghurt before and after fermentation on the physicochemical, microbiological and sensory characteristics of the yoghurt.
Procurement of raw materials
The turmeric rhizome (Plate 1), skimmed powdered milk, starter culture (Yoghurmet) and granulated sugar (Dangote Sugar Company) were purchased from Ogige main market in Nsukka local Government area of Enugu State, Nigeria.
Sample preparation
Preparation of turmeric extract
The turmeric was sorted, graded, washed thoroughly with water and the peel was separated from the flesh, milled and water was added for extraction as shown in Figure 1.
Preparation of ethanolic turmeric extract
180 g of ground spice was transferred to a 250ml conical flask. 200ml of 95% ethyl alcohol (ethanol) was added. The flask was covered, mixed, and stored overnight for 16 h at room temperature. The solution was filtered using a dry Whatman No. 1 filter paper. The ethyl alcohol was allowed to evaporate in a hot air oven at 110oC until a constant weight of the extract was obtained as shown in Plate 2A.
Preparation of aqueous turmeric extract
180 g of ground sample was weighed into a 500ml of conical flask. 200ml of water was added, covered and shaken vigorously. The flask was covered, mixed, and stored overnight for 16 h at room temperature. The solution was filtered using Whatman No. 1 dry filter paper, then dried in a hot air oven at 110oC until constant weight of extract was obtained as shown in Plate 2B.
Production of yoghurt
Yoghurt was produced as described by Lee and Lucey (2010) with slight modification. The milk mix was pasteurized at 80oC for 20 to 30 min to inactivate the pathogens in a Gallenkamp (220/240V, 50 Hz) water bath and homogenized at pasteurization temperature. The milk was cooled to inoculation temperature of 40 to 45oC and then inoculated with 2 to 3% starter culture (Yoghurmet consisting of Lactobacillus bulgaricus and Streptococcus thermophilus). The yoghurt was fermented for 12 h at incubation temperature of 43 to 45 oC in a water bath after which it was homogenized and divided into six portions. Thereafter, six sample blends of 95:5, 90:10, 85:15, 80:20, 75:25, 100:0 (Table 1) indicating the ratio of Yoghurt to Turmeric, were formulated as shown in Figure 2 and 3.
Sample analysis
Proximate composition of turmeric and formulated yoghurt
The moisture, crude protein (N x 6.25), crude fat, crude ash and crude fibre contents were determined using standard Association ofOfficial Analytical Chemists (AOAC, 2010).
Determination of total carbohydrate content
Total carbohydrate content was determined by difference (AOAC, 2005). This was simply carried out by subtracting the value of other food components (moisture, ash, fibre and protein) from 100 as shown in the Equation (1).
Determination of ash content
The ash content of the freshly prepared yoghurt and turmeric samples was determined according to the standards of AOAC (2010). A preheated and cooled crucible was weighed (W1) and 2 g of each of the samples was weighed into two preheated cooled crucibles (W2). The samples were charred on a Bunsen flame inside a fume cupboard. The charred sample in the crucible was then transferred into a preheated muffle furnace at 550oC for 2 h until a white or light grey ash was obtained (W3). It was then cooled in a dessicator, weighted and documented. The ash content of the samples was calculated using Equation 2
Effect of different levels of turmeric on the proximate composition of formulated stirred yoghurt
The significant (p < 0.05) increase in the moisture content of yoghurt samples formulated with graded levels of turmeric extracts when compared to the moisture content of the control sample (YOGHURT) could be traced to the reduction in the water holding capacity of milk by the extracts before fermentation. This observation was in agreement with the result obtained by Akande and Adegoke (2018) in which there was increase in moisture content of spiced yoghurt. According to Ammon et al. (1992), the marked increase in the moisture content of yoghurt formulated with spices could be attributed to the antibacterial mechanism exhibited by the spices involving formation of water in the electron transport system. For the yoghurt samples examined in this research, the protein contents of those samples with turmeric extracts (before and after fermentation) were lower than that of the plain yoghurt. This significant (p < 0.05) decrease could be traced to the presence of proteolytic enzymes (proteases) in the turmeric extract incorporated in the yoghurt samples which degrade proteins into peptides and amino acids. This assertion was in agreement with Nagarathnam et al. (2010). Altogether, the protein contents of the yoghurt samples did not exceed the commercial yoghurts’ recommended range (11-18%) of proteins prescribed by the National Yoghurt Association. Yoghurt, like ice cream, is a milk-and-water-based dairy product which is poor in fibre level (Cheeseman and Lean, 2000). Result showed that ash content decreased with increase in the amount of turmeric added. This is attributed to low ash content of the turmeric extract. The ash contents of the turmeric-containing yoghurt samples before and after fermentation were low compared to the plain yoghurt sample (without turmeric extract). This finding was in agreement with Akande and Adegoke (2018).According to U.S. Food and Drug Association, low fat yoghurt must contain 0.5 to 2% fat while regular yoghurt must be no less than 3.25% fat (Food Source Information – Colorado, 2018). The yoghurt samples examined in this study had low fat contents. This was attributed to the low fat content of the skimmed milk which was used as a major ingredient for yoghurts.The carbohydrate content of the yoghurt samples containing turmeric extracts increased with increase in the amount of turmeric added when compared to the carbohydrate content of plain yoghurt. This increase could be traced to carbohydrate present in the turmeric (Table 2).
Effect of different levels of turmeric on the physicochemical properties of the stirred yoghurt
The incorporation of turmeric extract in yoghurt before and after fermentation showed significant (p < 0.05) increase in pH leading to decrease in acidity. This observation could be attributed to the alkaline nature of turmeric itself. Decrease in viscosity was observed in the viscosity of stirred yoghurt formulated with turmeric extract as compared to the value obtained for the plain yoghurt sample. This observation correlates with high moisture content of the yoghurt samples in which turmeric extracts were incorporated. Thus, the higher the moisture content, the less viscous the samples become (and vice-versa).
Effect of different levels of turmeric on the micronutrient composition of the stirred yoghurt
The incorporation of turmeric extract (before and after fermentation) at different levels in the stirred yoghurt samples showed significant (p < 0.05) improvement in the vitamin B2, B3, and B12. However, vitamins C and B6 contents of each of the stirred yoghurt samples formulated with turmeric extracts (Plate 3) significantly decreased with increase in the levels of turmeric. The significant increase (p < 0.05) in vitamins B2, B3, and B12 could be attributed to the starter culture used in the stirred yoghurt samples. Lactic acid producing bacteria have been reported to produce or utilize B-group vitamins to meet their nutritional requirement during fermentation (Snell, 1993). The turmeric extract incorporated in the stirred yoghurts have been discovered to be rich in B-group vitamins especially vitamins B2, B3, and B12 and some mineral elements (Table 2). So, the contributions from turmeric extract in the stirred yoghurt and starter culture during fermentation could be categorically pointed to as the factors leading to the significant (p < 0.05) improvement of vitamins B2, B3, and B12in the stirred yoghurt samples. Calvince et al. (2019) reported that fermentation caused marked increase in niacin (vitamin B3) of milk. This is consistent with the result of Gu and Li (2016).
Capozzi et al. (2012) explained that B-group vitamins are present in a number of foods but are easily destroyed or removed during food processing and that succinctly explains why their deficiencies are commonly found a large population. Vitamins C and B6 decreased with increasing concentration of turmeric in the stirred yoghurt samples. These vitamins are heat-labile and can be destroyed or removed during pasteurization (80 to 85oC) and inoculation (40 to 45oC). Moreso, vitamins C and B6 are vital nutritional requirements for lactic acid bacteria (LAB). The more the lactic acid bacteria present in the sample, the less the amount of vitamins C and B6 turnout.
From the mineral analysis of the samples, there were significant (p < 0.05) improvement in the Calcium (Ca) and Phosphorus (P) of the stirred yoghurt samples wherein turmeric were incorporated. The aforementioned deductions corroborate with the reports of Hale et al. (2010), Ihemeje et al. (2015) and Mbaeyi and Anyanwu (2010). The results agreed with the assertion of Gray (2007) in which the author reported that yoghurt is a good dairy product and a source of indispensable minerals required for human metabolism and cells’ functionality.
Effect of different levels of turmeric on the Microbial qualities of the stirred yoghurt
The total viable count, coliform count, Lactic Acid Bacteria (LAB) count and mould count of the stirred yoghurt samples formulated with turmeric extracts were compared to study the effect of addition of turmeric extract before fermentation and after fermentation, with the plain yoghurt sample. When compared with the plain yoghurt sample, the mould count of the yoghurt-turmeric samples before fermentation decreased from 2.1 × 101to 0.1 × 101then became undetectable as the levels of turmeric increased. Similar trend was observed after fermentation where the mould count decreased from 5× 101to 4 × 101then became not detectable (ND) at 0.3, 0.4 and 0.5% of turmeric extract incorporated. This could be traced to the antimicrobial effect of turmeric extract on the samples. This finding was in line with the report by Akande and Adegoke (2018) on production, microbiological and quality evaluation of low-fat spiced yoghurts with low glycemic loads. The total viable count of the samples decreased far more before fermentation (1.9 × 105 to 1.2 × 105)than what it was after fermentation (2.0 × 105 to 1.5 × 105). Fermentation increased the amount of viable microorganisms in the samples. The total viable count levels are very much below the acceptable range (0.0 - 8.7 cfu) according to National Yoghurt Association (NYA, 2000).Similar trend as the mould count was obtained for the coliform count of the samples. Upon the incorporation of turmeric extract, the samples’ coliforms decreased to a non-detectable level before and after fermentation. It has been suggested that yoghurt should contain abundant and viable organisms of starter origin or above 1.0 x 104cfu/ml of the starter culture organisms (FAO and WHO, 2003) and, whichever format is adopted, there is a general agreement that yoghurt should contain live bacteria unless specifically designated as pasteurized or heat treated (Tamime and Robinson, 2007). Thus the values were consistent with the standard. Generally, total viable count and lactic acid bacteria count decreased with increase in concentration and this could be attributed to the conditions of fermentation which did not favour the rapid growth of microorganisms.
Effect of different levels of turmeric on the sensory characteristics of the stirred yoghurt
There were significant (p<0.05) differences in colour, taste aftertaste, consistency, firmness and overall acceptability (Table 7). The sample YTB1 (95:5) scored the highest for colour (8.24±0.01), while the sample YTA5 (75:25) within the stirred yoghurt group, had the lowest score (5.43± 0.01).The plain yoghurt scored (7.93±0.01).There was a decrease in the acceptability of colour as higher amount of turmeric added this is attributed to high intense of colour in the sample due to the effect of curcumin a colouring agent in the turmeric extract. The sample YTB1 (95:5) scored the highest for taste (8.87± 0.01), while the sample YTA5 (75:25) within the stirred yoghurt group had the lowest score (5.63± 0.01).The plain yoghurt scored (7.23± 0.01) for taste. There was a decrease in the acceptability of taste ashigher amount of turmeric was added. This could be attributed to high intense of the spice taste of turmeric impacting a bitter taste in the sample. The plain yoghurt scored the highest in consistency (8.13± 0.01) and firmness (8.21± 0.01), and the sample YTA5 (75:25) had the lowest in consistency (5.28± 0.01) and firmness (5.53± 0.01). This was evident in that, higher amount of turmeric reduces the consistency and firmness of the stirred yoghurt. The sample YTB1 (95:5) has the highest score in the overall acceptability of the whole samples.
Comparison of the extract of aqueous and ethanolic extraction
Tables 2 and 3 shows selected chemical components and characteristics of turmeric extracted with ethanol and water (as shown in Plate 2A and B). Turmeric extracted with ethanol had higher chemical composition and characteristics than the turmeric extracted with water. This could be attributed to the fact that curcumin (C21H20O5), the major bioactive compound in turmeric, is highly soluble in ethanol, acetone and dimethysulfoxide (Remadevi et al., 2007). It can then be inferred that turmeric is an oil-soluble, hydrophobic pigment which is practically insoluble in water (Tonnesen, 2002). Hence turmeric extracted with ethanol was used for the production.
Proximate composition of yoghurt graded with different levels of turmeric
Effect of turmeric extract on the moisture and protein contents of the stirred yoghurt
Table 4 shows that the moisture content values of plain yoghurt sample (without turmeric) were found to be 8.55±0.01%. Generally, there were significant (p<0.05) differences between the moisture content of the stirred yoghurt at different levels of turmeric incorporated. The moisture contents of samples ranged from 8.55±0.01 to 87.29±0.01%. Sample YTB5 (75:25) yoghurt to turmeric ratio before fermentation had the highest moisture content while the control Yoghurt (100:0) had the lowest moisture content. There was significant (p<0.05) difference in the protein content of the stirred yoghurt formulated with different amount of turmeric (Table 4). The values ranged from 2.64±0.05 to 4.13±0.01%. Sample YTB5 (75:25) yoghurt to turmeric ratio before fermentation had the lowest protein content while theplain yoghurt had the highest protein content. The effect of the different amount of turmeric also shows significant (p<0.05) differences at different levels. This is evident that protein content decreased with increase in the amount of turmeric added due to the fact that turmeric contains low protein content.
Effect of turmeric extract on the ash and fat contents of the stirred yoghurt
Data presented in Table 4 illustrated that there were significant (p<0.05) difference in the ash content of the stirred yoghurt at different levels of turmeric incorporated into the product. The ash content values were within the range of 0.20±0.01 to 1.81±0.01%. Yoghurt sample YTA5(75:25), that is, yoghurt samples with 0.5% turmeric extract after fermentation, had the lowest ash content while Yoghurt (100:0), the control sample, had the highest fat content. Notably, the ash contents of the yoghurt samples before and after fermentation decreased with increasing levels of turmeric extracts in the formulation. The effect of turmeric extracts incorporated on fat contents of the yoghurt samples was studied at different levels (0.1, 0.2, 0.3, 0.4 and 0.5%). The results revealed that significant (p<0.05) difference between the fat contents of the stirred yoghurt with different amount of turmeric existed (Table 4). The fat contents were within the range of 1.53±0.02 to 1.81±0.02%. Sample YTB5 (75:25) had the lowest fat content while Yoghurt (100:0) had the highest fat content.
Effect of turmeric extract on the carbohydrate content of the stirred yoghurt
Table 4 showed that there was significant (p< 0.05) difference between the carbohydrate contents of the stirred yoghurt samples and the different amount of turmeric extracted added (Table 4). The carbohydrate content ranged from 7.82±0.01 to 8.26±0.04%. The obtained results showed that sample YTB5(75:25) before fermentation had the highest carbohydrate content while the plain yoghurt (100:0), that is, the control sample, had the lowest carbohydrate content. In general, the effect of the different amount of turmeric also showed significant (p <0.05) differences at different levels.
Effect of turmeric extract on micronutrient contents of the stirred yoghurt
Effect of different amount of turmeric on vitamin B3 and vitamin B12 content of the stirred yoghurt: Table 5 showed that there was significant (p< 0.05) difference in vitamin B3 content of the stirred yoghurt with different amount of turmeric (Table 5). The samples ranged from0.12±0.00 to 1.72±0.01 mg. Sample YTA5(75:25) before fermentation had the highest vitamin B3 content while sample YTB1(95:5) had the lowest vitamin B3 content. Generally, the yoghurt samples formulated with turmeric before and after fermentation (YTB and YTA) have higher vitamin B3 content than the plain yoghurt (YOGHURT). There was a significant (p<0.05) difference in the vitamin B12 content of the stirred yoghurt with different amount of turmeric (Table 5). The samples ranged from 8.42±0.04 to 34.30±0.01µg.Sample YTA5(75:25) yoghurt to turmeric ratio before fermentation had the highest vitamin B12 content while plain yoghurt had the lowest Vitamin B12 content.
Effect of turmeric extract on vitamin C and vitamin B2 of the stirred yoghurt: There was a significant (p< 0.05) difference between vitamin C content of the stirred yoghurt and different levels of turmeric incorporated (Table 5). The samples ranged from 42.5±0.06 to 66.15±0.10 mg. Sample YTA1 (95:5) had the highest vitamin C content while the control sample (YOGHURT) had the lowest vitamin C content. The effect of the different amount of turmeric also shows significant (p <0.05) differences at different levels. Vitamin C content decreased with increase in the amount of turmeric. There was significant (p<0.05) difference in the vitamin B2 content of the stirred yoghurt with different amount of turmeric (Table 5). The samples ranged from 6.30±0.01 to 14.40±0.02 mg. Sample YTB5 (75:25) had the highest vitamin B2 content while plain yoghurt had the lowest vitamin B2 content.
Effect of turmeric extract on vitamin B6, calcium and phosphorus of the stirred yoghurt: There was significant (p<0.05) difference in the vitamin B6 content of the stirred yoghurt with different amount of turmeric (Table 5). The vitamin B6 content of the samples were within the range of 0.12±0.01 to 0.60±0.01 mg. Sample YTB1 (95:5) had the highest vitamin B6 content while plain had the lowest vitamin B6 content. The values of Calcium in the samples ranged from 85.90±0.01to 110.09±0.01mg.The calcium content of the stirred yoghurt showed significant (p< 0.05) difference at different levels of turmeric extract incorporated (Table 5). It was observed that sample YTA5 (75:25) had the highest calcium content as compared to sample yoghurt (100:0) which was found to have the lowest calcium content. This equally shows that yoghurt itself contains high amount of calcium which is necessary in young and adult for good bone and teeth development. Based on data presented in Table 5, there were significant (p<0.05) difference in the phosphorus content of the stirred yoghurt at different levels of turmeric extracts added. The phosphorus in the yoghurt samples ranged from25.60±0.01 to 87.29±0.00 mg. Sample YTA1 (95:5, that is, yoghurt to turmeric ratio before fermentation) had the highest phosphorus content while the control sample (Yoghurt) had the lowest phosphorus content. It was noted that for all samples in which turmeric extract was added, the phosphorus content decreased with increased level of turmeric before and after fermentation.
Effect of turmeric extraction on the physicochemical properties of the stirred yoghurt
Effect of turmeric extract on the pH and viscosity of the stirred yoghurt: Table 6 shows the pH and viscosity of the yoghurt samples in which turmeric extract was incorporated and the pH and viscosity of yoghurt sample without turmeric (that is, the control). The values for pH ranged from 4.68±0.02 to 5.21±0.07 (Table 6). Within the yoghurt, the pH increased with increase in the amount of turmeric added. This indicates that the addition of turmeric significantly increased the pH of the stirred yoghurt. Data presented in Table 6 also showed that all samples except sample YTB1 (95:5) had pH values significantly higher than that of the plain yoghurt. Considerable increase in pH of the yoghurt samples was also observed when pH of the samples before and after fermentation was compared. The values for viscosity ranged from 90.92± 0.17to 120.65 ± 0.20cP.Within the yoghurt, the viscosity decreased with increase in the amount of turmeric added.
Effect of turmeric extract on the microbial characteristics of the stirred yoghurt: Table 7 shows the total viable count, lactic acid bacteria, mould and coliform counts of the formulated stirred yoghurt.The mould count ranged from 3.0 x101cfu/ml in the plain yoghurt to a non-detectable (ND) amount in the sampleYTB5(75:25) where turmeric extract was added before fermentation. The plain yoghurt, that is, Yoghurt (100:0) had the highest mould count while sample YTB5(75:25) had the lowest mould count. The total viable count (TVC) was within the range of 1.2×105to2.2 ×105cfu/ml. The plain yoghurt was found to have the highest TVC (2.2×105cfu/ml) while sample YTB5 (75:25) gave the lowest total viable count. Also, the Coliform Count of the yoghurt samples ranged from 0.4×10 to 1.4×10cfu/ml. The lactic acid bacteria (LAB) Count of the samples ranged from 1.0 x105 to 2.1 x105cfu / ml. Generally, total viable count (TVC), mould count, and coliform count decreased with increase in the amount of turmeric added this could be attributed to anti-oxidant properties of turmeric extract.
Effect of different amount of turmeric on the sensory scores for stirred yoghurts: There were significant (p<0.05) differences in colour, taste aftertaste, consistency, firmness and overall acceptability (Table 8). The plain yoghurt was most appealing (8.23±1.45) as having the highest score while sample YTA5 (75:25) had the lowest score (5.43±0.91).Data obtained also revealed that there was a decrease in the acceptability of colour as the level of turmeric added increased (Table 8).
This could be attributed to high intense colour in the samples due to the effect of curcumin, a colouring agent in the turmeric extract. The sample YTB1 (95:5) scored the highest for taste (8.87±0.49), while the sample YTA5 (75:25) within the stirred yoghurt group had the lowest score (5.23±1.07).The plain yoghurt scored (7.23±1.48) for taste. There was a decrease in the overall acceptability of taste as higher amount of turmeric was incorporated. This could be traceable to a very characteristic spicy taste of turmeric in the samples thus changing the samples’ taste from sweet to somewhat bitter taste. The sample YTA1(95:5) scored the highest in consistency (8.45±1.26) and the sampleYTA5 (75:25) had the lowest in consistency (5.21±1.57). The panelists rated sample YTB1 (95:5) highest (8.43±0.98) while sample YTB5(75:25) had the lowest score (5.21±0.26) for firmness. This was so evident that the higher amount of turmeric reduced the consistency and firmness of the stirred yoghurt. The plain yoghurt (100:0) sample had the highest score in the overall acceptability (8.86±0.84) while sample YTB5 (75:25) had the lowest score (5.67±1.00). Samples YTB5 (75:25) and YTB3 (85:15) had the lowest (5.24±0.50) and highest score respectively for after taste.
This study shows that turmeric extracted with ethanol have higher nutrient composition than turmeric extracted with water. The different concentrations of turmeric affected the nutritional composition of the yoghurt. pH increased with increase in concentration of the turmeric due to the alkalinity of the turmeric. The use of turmeric affected the colour of the yoghurt, changing it from white to yellowish-orange due to the curcumin in the turmeric. Although the protein and carbohydrate contents of the yoghurt samples formulated decreased with increasing concentrations of turmeric, the minerals (calcium and phosphorus) and vitamins (B2, B3, and B12) improved significantly (p < 0.05) between the range of 100:0 to 75:25 before and after fermentation. There was a decrease in microbial load of the yoghurt as the concentration of turmeric increases due to the fact that turmeric possesses antimicrobial ability thus increasing the keeping quality of the yoghurt. In terms of overall acceptability, the stirred yoghurt sample with 0.1% turmeric (that is, YTB1 (95:5) was most preferred sample. Therefore, the yoghurt: turmeric concentration of 90:10 and less should be used to achieve the taste effect and colour of the stirred yoghurt.
The authors declare no conflict of interest.
The authors would like to appreciate Prof. T.M. Okonkwo of the Department of Food Science and Technology, University of Nigeria Nsukka for his support and encouragement.
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