Changes in pectinases, dietary fibers, and physicochemical indices related to the flavor of cubiu fruits during ripening

The objective of this study was to evaluate the changes in the activity of pectinases (pectinesterase and polygalacturonase), dietary fiber content (alcohol-insoluble solids, pectin, and total fiber), and physicochemical indices related to the flavor (pH, titratable acidity, soluble solids, Brix/acid ratio, and reducing and nonreducing sugars) of cubiu fruits (Solanum sessiliflorum Dunal) at different stages of ripening (green, turning, ripe, and fully ripe). Alcohol-insoluble solids and pectin were very similar, with the highest levels detected at the green and turning stages, and the lowest levels occurring at the fully ripe stage. The amount of total fiber was consistent at the green, turning, and ripe stages, but declined at the fully ripe stage. These changes correlated with the pectinase activities, the profiles of which resembled those of other species of the Solanaceae family during fruit ripening. However, cubiu fruits were significant sources of dietary fiber at all stages. The reducing sugar content reached the highest level at the turning stage, with glucose as the major sugar. The content of nonreducing sugars, such as sucrose, remained low at all stages. The other physicochemical indices displayed increases during ripening, characterizing cubiu as a very acidic fruit with a small degree of sweetness.

本研究旨在评估不同成熟阶段（青果期、转色期、成熟期与完熟期）的cubiu果实（Solanum sessiliflorum Dunal）的果胶酶（pectinases）活性（包含果胶酯酶（pectinesterase）与多聚半乳糖醛酸酶（polygalacturonase））、膳食纤维（dietary fiber）含量（包括酒精不溶固形物（alcohol-insoluble solids）、果胶与总膳食纤维（total fiber）），以及与风味相关的理化指标（pH值、可滴定酸度（titratable acidity）、可溶性固形物（soluble solids）、糖酸比（Brix/acid ratio）、还原糖（reducing sugars）与非还原糖（nonreducing sugars））的变化规律。其中，酒精不溶固形物与果胶的含量变化趋势高度一致，二者均在青果期与转色期达到峰值，完熟期降至最低水平；总膳食纤维含量在青果期、转色期与成熟期保持相对稳定，但在完熟期出现下降。上述含量变化与果胶酶活性变化呈显著相关，其活性变化模式与茄科（Solanaceae family）其他物种果实成熟过程中的表现类似。不过，cubiu果实于各成熟阶段均为优质膳食纤维来源。还原糖含量在转色期达到峰值，且以葡萄糖为主要糖分；蔗糖等非还原糖含量在各成熟阶段均维持在较低水平。其余理化指标随果实成熟进程逐步升高，表明cubiu果实酸度较高、甜度较低。