Nonenzymatic Browning Of Pineapple Juice Concentrates During Storage

Kinetics of nonenzymatic browning in pineapple juice concentrates (pineapple flesh juice concentrate, pineapple whole fruit juice concentrate) during storage were investigated. This paper studied the color stability, kinetics of color change, kinetics of Maillard reaction, and nonenzymatic browning reasons for the two kinds of juice concentrates during storage. The paper also studied the quality difference between the two kinds of products during storage and analysis the essential reasons. The main conclusions were made as follows:1) The values of browning index, pH, chlorophyll content, HMF, Vc, proanthocyanidin content and total phenols in pineapple flesh juice and pineapple whole fruit juice concentrates were not different significantly at the 0.05 level, but for anthocyanins. The difference of color was not significant as observed by the naked eye.2) Nonenzymatic browning in pineapple juice concentrates were more serious during storage. Activation energies for nonenzymatic browning of pineapple flesh juice and pineapple whole fruit juice concentrates were 74.35 and 59.95kJ/mol, respectively. Activation energies of pineapple whole fruit juice concentrate was lower, which means it has the higher activity of nonenzymatic browning. The equations:(1) lnk=26.837-74.35/RT and (2) lnk=21.641-59.9/RT were kinetic models of color change for pineapple flesh juice and pineapple whole fruit juice concentrates, respectively.3) The Maillard reaction was fitted well to first-order kinetic model during storage. The formation of HMF occurred in pineapple juice concentrate stored at 37℃, but not be determined in samples stored at 5 and 18℃. HMF levels accelerated the nonenzymatic browning and which accelerated the nonenzymatic browning mainly at the later storage period when storage at 37℃. There is no distinct difference about rate constants of HMF between pineapple whole fresh juice and pineapple fresh juice concentrates, so Maillard reaction was not the major reasons for the quality difference between them.4) The degradation of total phenols and Vc, and accumulation of anthocyanins all acceleratrd the nonenzymatic browning during storage, and the accumulation of anthocyanins and degradation of Vc maybe were the major reasons for the quality difference between two kinds of juice concentrates.5) Through path coefficient analysis between nonenzymatic browning factors and chromatism, some useful conclusion was gotten: (1) Accumulation of anthocyanins was the essential reason of quality difference for the two kinds of products during storage at 18℃; and the accumulation of anthocyanins not only effect directly for nonenzymatic browning in pineapple whole fruit juice concentrate, but also was a chief element for deciding nonenzymatic browning. (2) The interaction between anthocyanins and Vc was a chief element for deciding the nonenzymatic browning in pineapple whole fruit juice concentrate during storage at 37℃. So the higher initial content and accumulation rate of anthocyanins effect the quality of pineapple whole fruit juice concentrate, anthocyanins was the most important factor for its quality degration.