Studies Of Factors Influencing Non-enzymatic Browning Of Apple Juice Concentrate

Studies were carried out on processing indexes of fruits, the changes of A420, color aberration values,5-hydroxymethyl furfuraldehyde(5-HMF), reductive sugars and amino acids contents of apple juiceconcentrates of hybrids(95-32,95-33,95-51,95-70,95-124,95-153) during the course of storage,and influences of temperature, pH, sugar(soluble solid substance) content and degree of fruit maturation onnon-enzymatic browning of apple juice concentrate of Lujia4 (95-76). All the hybrid apple trees werederived from two crosses (Telamon×Starkrimson, Telamon×Fuji). Maillard reactions caused by amino acidsand reductive sugars were simulated in citric acid-phosphate buffer(pH3.2)and in apple juice concentraterespectively. The main results were as follows:1. There were great differences among processing indexes of different genotypes in apple. The timesof fruit maturation of strains (95-32, 95-70 ) were late, and sugar (soluble solid substance) contents of fruitswere high, and PPO activities, △ A420 and △ T625 values were low;Times of fruit maturation of strains(95-51, 95-153 ) were early, and sugar (soluble solid substance) contents of fruits were low, and PPOactivities, △ A420 and △ T625 values were high.The time of fruit maturation had an obvious effect on sugar (soluble solid substance) content of fruit.Early ripening fruits tended to be browning easily. Enzymatic browning in juice processing had asignificant effect on non-enzymatic browning of apple juice concentrates during the course of storage.2. Color aberration values of different genotype apple juice concentrates were increased with the lengthof duration of storage, but those of strains (95-32, 95-70 )apple juice concentrates rose slowly, and those ofstrains (95-51, 95-153) apple juice concentrates rose quickly during the course of storage. 5-HMF contentsof strains (95-32, 95-70 )apple juice concentrates rose first, then descended, and rose again, and those ofstrains (95-33, 95-124 )apple juice concentrates rose first, then descended, but those of strains (95-51,95-153 )apple juice concentrates descended first, then rose;Peak values of 5-HMF contents were quitedifferent among different genotype apple juice concentrates. The highest values were found in strains(95-33, 95-124) apple juice concentrates, and the lowest values were found in strains (95-32, 95-70) applejuice concentrates. Change trends of reductive sugars contents were mere less the same expect for 95-32,and reductive sugars contents rose first, then descended, rose and descended again. Lysine, phenylalanine,leucine, isoleucine, methionine and threonine contents of apple juice concentrates had declined during thecourse of storage.3.Temperature had a great effect on non-enzymatic browning of apple juice concentrate during thecourse of storage, and the higher temperature was , the more evident non-enzymatic browning of applejuice concentrate was;Sugar content also had a great effect on non-enzymatic browning of apple juiceconcentrate, and the higher sugar content of apple juice concentrate was, the more evident non-enzymaticbrowning of apple juice concentrate was;pH and fruit maturation degree significantly affectednon-enzymatic browning of apple juice concentrate as well, and pH was positively correlated with A420within 2 weeks during the course of storage at 25oC, whereas pH was negatively associated with A420 after2 weeks storage. Juice output ratio, soluble solid substance content, polyphenol content of fruit, and acidcontent of apple juice concentrate varied with degree of fruit maturation. Light non-enzymatic browningapple juice concentrate was found with fully matured fruit.4.In the simulations of maillard reation activities of both amino acids and reductive sugars in applejuice concentrate were higher than those in citric acid-phosphate buffer(pH3.2). Simulation experiment inapple juice concentrate seemed to be more suitful for detecting the reality between amino acids andreductive sugars reation than that in citric acid-phosphate buffer(pH3.2). Reation activity of lysine inamino acids was the highest in amino acids tested.