Research On Non-enzymatic Browning Factors And Control Of Pear Juice Concentrate

Pyrus spp pear is one of five yield fruits in China, and has rich varieties resources. Pear juice concentrate is the major process and export products. But it is easily happening non-enzymatic browning, affect the Pear juice concentrate quality and market. In-depth study of pear juice concentrate non-enzymatic browning and control factors have theoretical and practical significance on elucidate the law of non-enzymatic browning, promoting pear juice concentrate process industry and technology development, improving the products quality. In this paper, our country′s major pear as raw materials was used, researched on the characteristics and factors on non-enzymatic browning in different varieties of pear juice concentrate processed. Changes of the non-enzymatic browning factors of six varieties of pear juice concentrate storaged at different temperatures were studied. Path analysis was used to discuss the reasons of non-enzymatic browning. Studied on the changes of sugar and amino acid species and contents in Changba pear juice concentrate during storaged, preliminary studied on add sulfur amino acids inhibit the juice browning effect. The main results and conclusions were as follows.1. The characteristics and factors on non-enzymatic browning in different varieties of pear juice concentrate processed. Compared with normal pressure concentration, reduced pressure concentration was beneficial to control the non-enzymatic browning. In addition, the lower the temperature was, the more obvious the depression effected of the non-enzymatic browning. Results indicated that with the concentration temperature increased, the polyphenol content and colour value of the concentrated juice increased, the reducing sugar content and amino nitrogen content decreased. 50℃was the optimal temperature of reduced pressure concentration.2. The characteristics and factors on non-enzymatic browning in different varieties of pear juice concentrate storaged. The browning degrees among six pear juice concentrates with significant difference storage temperature and time of positively correlated, The browning of Fengshui pear, Shuijing pear juice concentrate during storage was serious, Changba pear and Ya pear juice concentrate was lighter, the browing speed rate slowly, benefited for long-term storage. The differences of browning related indexes among six pear juice concentrates storageed at 25℃were obvious. The polyphenols content and amino nitrogen content decreased. Changba pear juice concentrate with higher levels of polyphenols and titratable acids, pH and amino nitrogen content was smaller, the minimum titratable acid content in Huangguan pear juice concentrate, higher levels of amino nitrogen content in Ya pear and Fengshui pear juice concentrate. With the storage temperature increased, the polyphenols content, reducing sugar content and amino nitrogen content decreased. Browning was lesser at low temperature storage, and the non-enzymatic browning basic did not happened in the main at frozen storage. Within the scope of certain, reduced pH makes for inhibiting the reaction rate of non-enzymatic browning. Especially at pH 2.5, it much more inhibited the non-enzymatic browning. Appropriated to reduce the pH of pear juice concentrate,storaged below 5℃could beneficial to inhibited non-enzymatic browning.3. Non-enzymatic browning reasons for the pear juice concentrate during storaged. The interaction between amino nitrogen and polyphenols was a chief element for deciding the browning in Ya pear juice concentrate during storaged at 5℃. Amino nitrogen played the most direct role for the degree of the browning of Ya pear juice concentrate, reducing sugar was the second direct influencing factor. The chief affected of Changba pear juice concentrate was polyphenols, followed by amino nitrogen. The interaction between amino nitrogen and polyphenols was a chief element for deciding the browning in Ya pear, Changba pear and Huangjin pear juice concentrate during storaged at 25℃, Shuijing pear juice concentrate direct influencing factor was amino nitrogen, amino nitrogen played the most direct role, polyphenols was the second direct influence for the degree of browning of Ya and Changba pear juice concentrate and reducing sugar for Shuijing and Huangjin pear. The interaction between polyphenols and reducing sugar was a chief element for deciding the browning in Fengshui and Huangguan pear juice concentrate, the chief effect of Huanguan pear juice concentrate was polyphenols, followed by reducing sugar, and the chief effect of Fengshui pear juice concentrate was reducing sugar, followed by polyphenols.4. The substrate changed of Mailard reaction and the browning controlled of Changba pear juice concentrate during storaged. The main sugars in Changba pear were sucrose, glucose, fructose, xylose and lactose, and reduction of the total sugar occured in this storaged, Aspartic acid, glutamic acid and serineare are the major components of the 14 free amino acids of the Changba pear. The total amino acids was less decrease storaged at 5℃, a decrease of approximately 26% when storaged at 25℃for six months, including aspartic acid, glutamic acid, alanine, proline and lysine content decreased, serine, threonine, leucine and other content were not changed. Add Cys in pear concentrate juice could reduce the length of the non-enzymatic browning rate, add 0.5g/L Cys to the concentrated juice made the lightest browning, but Methionine had no inhibition.