Research On Hard Cheese Processing Technology And Flavor Compounds

The experiment aimed to explore a kind of cheese,water content wascontrolled in the range of hard cheese by drying at40℃, the maturity was largelyshorten, and the cost of mature was reduced.The flavor was milder, it is easier tobe accepted by domestic consumers.Firstly, the response surface method was used to optimize the hard cheeseprocessing technology. Secondly, variation in its physical and chemical indicatorsof the maturation process was measured to explore the best maturity. Finally,flavor compounds were studied. The main results are as follows:1. The process technical of hard cheese was optimized to confirm the bestprocessing parameter. The best process parameter was2.5%starter content,0.02%calcium chloride content,0.002%rennet content,0.5g/100mL saltcontent, and40min fermenting time. Under this condition, the cheese tastespleasant, swells fragrant, looks good, and the texture is tight and elastic.2. Moisture, pH,protein (pH4.6SN,12%TCA), amino nitrogen, free fattyacids, pHysical and chemical indicators were measured, the results indicated that:with maturity prolonged, moisture showed an upward trend; pH value showed anupward trend after the first drop; casein occured strongly hydrolyze, pH4.6SNand12%TCA SN showed a significant growth trend, it degraded fast inpre-mature stage, degraded slow in the late mature; content of free aminoacids,and free fatty acids were also significantly increased; TPA indicators all hadreduce in different degree. Combined with sensory evaluation， the hard cheeseobtained the best mature time,it was21days.3. Headspace solid phase micro extraction with GC-MS technique(SPME/GC-MS) was used to isolate and identify their volatile flavor compounds.It was detected42kinds of volatile flavor compounds, including carboxylic acids,alcohols, ketones, aldehydes, esters, hydrocarbons, heterocyclic compounds andso on. The best extraction condition for Solid phase micro extraction was:equilibrium time30min, extraction time30min, extraction temperature at50℃. 4. Seventeen kinds of free amino acids were detected by HPLC, and peakarea normalization method was used to determine the relative percentages ofvarious types of amino acids. The results showed that: although present umamiand bitter amino acid content is high, the sweet and sour amino acid content isalso relatively high, it can mask the bitter taste caused by the bitter amino acids ina certain extent, flavor acids promote the overall flavor of the cheese.5. Ten kinds of free fatty acids were detected by GC-MS, and peak areanormalization method was used to determine the relative percentages of varioustypes of fatty acids. The results showed that: myristic acid, palmitic acid, oleicacid content was high, it accounted for more than60%of the total free fatty acids,these long chain fatty acids made the whole of the cheese flavor more rounded.The cheese is rich in essential fatty acid, such as oleic acid and arachidonic acid,they improve the nutritive value of cheese.