Physico-chemical characteristics of set type yogurt

Yogurt is a popular dairy product among other dairy and food products and excessively used worldwide. Yogurt manufacturing is dependent on various factors.

Among all these, the most important are, starter culture, sources and quality of milk, incubation time and temperature. Therefore, it is a dire need of the time to optimize industrial processing for yogurt manufacturing keeping in mind all the above-mentioned factors which effects the quality of yogurt.

This study has been planned to determine the effect of milk quality, concentration of starter culture and incubation temperature on physico-chemical characteristics of yoghurt.

Sahiwal and Holstein Friesian milk procured from Dairy Animal Training and Research Center, B-block University of Veterinary and Animal Sciences, Pattoki and Nili Ravi Buffalo milk procured from Buffalo Research Institute. Yoghurt prepared from milk of buffalo, Sahiwal and Friesian and their blends at 50:50% concentrations, keeping buffalo milk as control. Textural characteristics such as gel firmness, viscosity, pH, syneresis and sensory evaluation determined at 0, 7, 14 and 21 days. In second experiment, effect of concentration of culture on incubation time, storage and sensory characteristics of set yogurt studied. Effect of 0.9, 1 and 1.1 (culture units/10 liter) studied in yoghurt prepared from milk of buffalo, Sahiwal and Friesian and their blends at 50:50% concentrations.

Textural characteristics such as gel firmness, viscosity, pH, syneresis and sensory evaluation determined at 0, 7, 14 and 21 days. In third experiment, effect of incubation temperature (38, 43 and 48oC) studied in yoghurt prepared from milk of Nili Ravi, Sahiwal and Friesian and their blends at 50:50% concentrations. Textural characteristics such as gel firmness, viscosity, pH, syneresis and sensory evaluation conducted at 0, 7, 14 and 21 days.

The gross composition of milk may affect the textural, compositional and microbiological properties of yoghurt. Some other managemental factors such as varying levels of fat contents due to breed, geographical location and feeding regime may significantly impact on the processing steps, product manufacturing and overall quality of the final product. Sahiwal, Holstein Friesian milk procured from Dairy Animal Training and Research Center, B-block University of Veterinary and Animal Sciences, Pattoki and Nili Ravi Buffalo milk procured from Buffalo Research Institute (BRI), Pattoki.

All other ingredients purchased from Sigma Aldrich Germany through local suppliers. Milk was standardized to 15% total solids with 3.5% fat. Skim Milk Powder (SMP) was used for the standardization of the yogurt. Milk was pasteurized at 82oC for 5 minutes and cool down to 43oC and at this temperature starter culture was added. Yogurt batch incubated at 43oC for 3 to 3.5 hours.

During this period pH was monitored regularly and as the pH drops to 4.6, the batch was shifted to blast chilling at 1-2oC and then stored at 4oC. Sensory evaluation of all yogurt samples was carried out on a 9-point hedonic scale. All the tests were carried out on day 0, 7, 14 and 21. The collected data was investigated through ANOVA technique under complete randomized design (CRD) using SAS 9.1 software. The results showed that yoghurt made from buffalo milk (To) showed a significant (p= 0.5) overall acceptability as compared to other treatments. Yoghurt made from buffalo milk (To) were followed by T3, T4, T1 and T5 respectively. The buffalo milk showed higher acceptability to the consumers.

Yogurt is a coagulated milk, mostly obtained by the action of two bacteria, Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. Yogurt is made of milk, considered as a complete food. It is mostly consumed by infants or elder people.

It contains all nutrition required by the people, along with this also contain live microbes. Sahiwal and Holstein Friesian Cow milk procured from Dairy Animal Training and

Research Center, B-block, University of Veterinary and Animal Sciences, Pattoki, Whereas Nili Ravi Buffalo milk procured from Buffalo Research Institute (BRI), Pattoki.

The experiment and analysis of the samples carried out in the Department of Dairy Technology A-Block, University of Veterinary and Animal Sciences, Pattoki. Milk standardized to 15% total solids (TS) with 3.5% fat. Skim Milk Powder (SMP) used for the standardization of the yogurt. Milk pasteurized at 82oC for 5 minutes and cool down to 43oC and at this temperature starter culture was added at 0.9%, 1% and 1.1% respectively. Yogurt batch incubated at 43oC for 3 to 3.5 hours. During this period pH monitored regularly and as pH drops to 4.6, the batch was shifted to blast chilling at 1-2oC and then stored at 4oC.

All the samples were analyzed for TS, fat, acidity, syneresis, viscosity and sensory characteristics at day 1, 7, 14 and 21 respectively. The results showed that yoghurt made from 1% culture were of high attributes as compared to 0.9 and 1.1% culture concentration. Milk source was also having a significant effect on yoghurt quality. Yoghurt made from 100% buffalo milk (To) with a culture concentration of 1% was of superior quality followed by T3, T4, T1, T5 and T2 respectively.

Yoghurt is made by the action of bacteria. These bacteria ferment the protein during the manufacturing of yoghurt. Lactose is converted into lactic acid before storage and to some extent after the storage. Yoghurt fermentation should be under controlled condition for the good and smooth texture of the final product. Sahiwal and Holstein Friesian Cow milk procured from Dairy Animal Training and Research Center, B-block, University of Veterinary and Animal Sciences, Pattoki. Whereas Nili Ravi Buffalo milk procured from BRI, Pattoki.

The experiment and analysis of the samples were carried out in the Department of Dairy Technology A-Block, Ravi Campus, University of Veterinary and Animal Sciences, Pattoki. Milk standardized to 15% total solids (TS) with 3.5% fat. Skim Milk Powder (SMP) used for the standardization of the yogurt. Milk pasteurized at 82oC for 5 minutes and cool down to 43oC and at this temperature starter culture added at 0.9, 1 and 1.1% respectively.

Yogurt batch incubated at 38, 43 and 48oC for 3 to 3.5 hours. During this period pH was monitored and as the pH drops to 4.6, the batches were shifted to blast chilling at 1-2oC and then stored at 4oC. Physico-chemical and sensory analysis were performed at day 1, 7, 14 and 21 respectively.

It was depicted from the experiment that 43oC with 1% culture of buffalo milk (To) showed best result as well as best consumer acceptability followed by T3, T4, T5, T1 and T2 respectively.