Fruit Quality and Antioxidant Properties in Alabama-Grown Blackberries During Fruit Maturation

Abstract

Changes in fruit quality attributes and antioxidative properties from six cultivars of thornless blackberries (Rubus sp.) (‘Apache’, ‘Arapaho’, ‘Chester’, ‘Loch Ness’, ‘Navaho’, and ‘Triple Crown’) during four different ripening stages (red, motded, shiny-black, and dull-black) were determined under Alabama growing conditions. Berry fruit samples were evaluated for pH, titratable acidity, total soluble solids, TSS/TA ratio, soluble sugars, vitamin C (reduced, oxidized, and total) and antioxidant capacity (measured as trolox equivalent antioxidant capacity, TEAC). Significant variation among cultivars and maturity of harvest were in fruit quality attributes and antioxidative properties found. An increase in fruit pH concomitant with a decline in titratable acidity (TA) was observed during ripening for all cultivars. Total soluble solids (TSS) values increased from 5.7 to 11.6%, and TSS/TA ratio ranged from 11.9 to 63.6. Highest reducing and total sugar content were contained in dull-black fruit. Vitamin C content either declined or remained unchanged with ripening and the pattern was dependent on cultivar, maturity at harvest. In general, antioxidant activity declined between red and dull-black ripening stages. The results indicate that TSS/TA ratio and TEAC were good indicators of fruit maturity and nutritional quality, respectively.     

基于微波干燥的黑莓介电特性研究

以黑莓为对象,利用网络分析仪测量并研究了频率（1～3 000 MHz）、黑莓含水率（20%～80%）和温度（20～100 ℃）对相对介电常数ε′和介质损耗因数ε″的影响;计算了微波穿透深度,并分析频率、含水率和温度对其的影响;建立了部分频率下黑莓介电参数与主要影响因素的关系模型,检验了基于介电参数预测含水率的精度和可行性。结果表明,在1～3 000 MHz频率段内,黑莓的介电常数ε′和介电损耗因子ε″都随频率的增大而减小;ε′随含水率的增大而增加,但随温度的增大而减小;ε″随含水率的增大而下降,但随温度的增大而增加;能量穿透深度随温度、频率的升高而降低,随含水率的升高而增加。可用二元二次方程描述介电参数和主要影响因素的关系,且各模型的决定系数皆大于0.96。所构建的模型可以很好地描述黑莓的介电参数与各主要影响因素的关系,说明基于介电参数和温度预测黑莓的含水率是可行的。