COMPARATIVE EVALUATION OF THE EFFECTS OF PRETREATMENTS ON THE NUTRITIONAL AND CHEMICAL PROPERTIES OF GINGER LEAF-BASED HERBAL TEA

There is increasing awareness and acceptance of herbal teas because of their contribution to nutrition and health. The use of ginger (Zingiber officinale) leaves as tea in some communities has been reported. While many research efforts have focused on ginger rhizomes, there is a limited report on ginger leaves’ nutritional, antioxidant properties and also what effect application of different heat pretreatments will have on the final product. The present study sought to develop a ginger leaf-based herbal tea and examine the effects of postharvest pretreatments such as steam blanching before drying, hot water blanching before drying and directly drying on the nutritional and chemical properties of the tea. Fresh green leaves were sorted, washed and drained. A batch of the leaves was evenly steam blanched at 1000C for 5 minutes before drying, another set was dipped in boiling water at 1000C for 3 minutes and the last batch was dried directly at 550C under standard conditions. The dried leaves were milled, packed in tea bags and a sample each was evaluated for its proximate, mineral, vitamin C, phytochemicals and antioxidant properties following standard procedures. The results showed that steam blanching significantly (p&lt;0.05) increased the protein, fat, sodium, potassium, saponin and the antioxidant potential (ferric reducing antioxidant power) compared to those that were hot water-blanched before drying and those dried directly. However, vitamin C, tannin, phytate, oxalate and zinc contents decreased significantly when compared with the fresh leaves. The free radical scavenging activity examined using DPPH activity, phenols and flavonoids did not vary significantly between the steam blanched and fresh leaves. These findings showed that steam blanching of ginger leaves before drying for consumption as a functional beverage is beneficial in terms of nutrient and antinutrient properties compared to hot water blanching before drying and direct drying. Therefore, this method of processing could be adapted for improved nutrition.草本茶因兼具营养与健康益处，大众对其认知度与接受度与日俱增。已有研究报道，部分社群将姜（Zingiber officinale）叶片用作茶饮原料。尽管现有研究多聚焦于姜根茎，但针对姜叶片的营养、抗氧化特性，以及不同热预处理方式对最终产品品质的影响，相关报道仍较为匮乏。 本研究旨在开发一款姜叶基草本茶饮，并探究三种采后预处理方式——干燥前蒸汽烫漂、干燥前热水烫漂、直接干燥——对该茶饮营养与化学特性的影响。实验选取新鲜翠绿的姜叶，经分拣、清洗与沥干后分为三组：第一组置于100℃下蒸汽烫漂5分钟后干燥；第二组浸入100℃沸水中共烫漂3分钟；第三组在标准条件下以55℃直接干燥。将干燥后的叶片粉碎装袋，随后按照标准流程分别检测各组样品的常规营养成分、矿物质、维生素C、植物化学物及抗氧化特性。 结果显示，与热水烫漂后干燥组及直接干燥组相比，蒸汽烫漂处理可显著提升样品的蛋白质、脂肪、钠、钾、皂苷含量与抗氧化潜能（铁还原抗氧化能力），差异均具有统计学显著性（p<0.05）。但与新鲜叶片相比，蒸汽烫漂组的维生素C、单宁、植酸、草酸及锌含量均显著下降。采用DPPH（1,1-二苯基-2-苦基苯肼）法检测的自由基清除活性，以及总酚、总黄酮含量，在蒸汽烫漂组与新鲜叶片组之间无显著差异。 本研究结果表明，相较于热水烫漂后干燥与直接干燥两种工艺，将姜叶片经蒸汽烫漂后再干燥以制备功能性饮品，在营养成分与抗营养因子特性方面更具优势。因此，该加工工艺可用于优化姜叶茶饮的营养品质。