枇杷果汁加工过程中产品品质的变化

在枇杷果汁加工过程中，对鲜果以及护色、打浆、酶解、过滤和调配等工艺环节处理后，分别取样测定其色差值、可滴定酸、可溶性固形物、总酚和黄酮的含量以及对2,2’-联氮-二（3-乙基-苯并噻唑-6-磺酸）二铵盐自由基（2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate) free radical，ABTS＋·）清除率，并采用顶空固相微萃取结合气相色谱-质谱分析技术，对挥发性物质进行富集、分离和鉴定，研究枇杷果汁加工过程中产品品质的变化。结果表明，枇杷果汁加工过程中的总色差值呈先升高后下降的趋势，其中酶解后其色差值最大；可溶性固形物和可滴定酸含量总体上先呈下降趋势，经调配处理后极显著上升；总酚和总黄酮含量以及对ABTS＋·清除率呈现下降趋势。从枇杷加工不同环节产品中鉴定出的挥发性化合物以醇类、醛类和酯类为主。主成分分析结果表明，枇杷鲜果、护色及调配后的产品具有较好的营养、口味、香气品质以及抗氧化性能，而打浆、酶解和过滤环节都在不同程度上严重降低了产品品质。

Quality Changes of Loquat Juice during Processing

To explore the quality changes of loquat juice during processing, samples were collected at different processing
steps of fresh harvested fruits, color fixation, pulping, enzymatic hydrolysis, filtration and blending for the measurements
of color parameters and soluble solid, titratable acid and total phenolics and total flavonoids contents as well as ABTS+·
scavenging capacity. Meanwhile, volatile compounds were extracted by headspace solid phase microextraction (SPME),
separated and analyzed by gas chromatography-mass spectrometry (GC-MS). Results showed that total color difference
exhibited an initial increase, reaching the maximum value after enzymatic hydrolysis, followed by a decrease during loquat
juice processing. Similarly, the contents of soluble solid and titratable acid also decreased first and then increased, with a
significant increase being noted after blending, while the contents of total phenolics and flavonoids and ABTS+· scavenging
capacity tended to decline. The main volatile compounds identified during loquat juice processing were alcohols, aldehydes
and ethers. Principal component analysis (PCA) showed the fresh fruits, the intermediate product after color fixation and the
final product had better nutritional, flavor and aroma quality as well as stronger antioxidant performance, while the steps of
pulping, enzymatic hydrolysis and filtration severely reduced the quality of products to different degrees.