DEVELOPMENT OF PROCESS PROTOCOL FOR DRYING OF STINGING NETTLE LEAVES Dr YASHWANT SINGH PARMAR UNIVERSITY OF HORTICULTURE AND FORESTRY SOLAN (NAUNI) HP partial fulfilment of the requirements for the degree MASTER OF SCIENCE DEPARTMENT OF FOOD SCIENCE AND TECHNOLOGY COLLEGE OF HORTICULTURE (Urtica dioica L.)
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Date
2021-11
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UHF,NAUNI
Abstract
ABSTRACT
Stinging nettle (Urtica dioica L.) family Urticaceae, is wild herbaceous, perennial, flowering
plant having Stinging hairs and commonly found in moist or damp soil which is native to Europe,
Asia, Northern Africa, America. It is known since ancient times as a wild source of food and herbal
medicine but the plant remained under-utilized due to inherent trichomes present in the leaves and
stems which are responsible for causing irritation to the skin. Drying of Stinging nettle leaves not only
allow their use when the plants are physiologically inactive but also extend the consumption period
and utilization at the time of food shortage especially for addressing micronutrient malnutrition. In
this study, Stinging nettle leaves were harvested at two stages viz. Tender leaflets from the top with
meristem and mature leaves. The initial physico-chemical analysis revealed higher quality of young
leaves with respect to higher crude protein (4.36%), ascorbic acid (57.82 mg/100g), antioxidant
activity (14.60%) and chlorophyll a (6.55 mg/l), chlorophyll b (2.07 mg/l), total chlorophyll (8.91
mg/100g). The effect of pre-treatment and drying of Stinging nettle leaves (viz. cabinet dried and
vacuum dried) on chlorophyll a and b, ascorbic acid and total phenol content as well as antioxidant
activity, were investigated. Blanching of Stinging nettle leaves include water blanching and steam
blanching, but the central composite design using response surface methodology revealed that water
blanching using 0.15% MgO along with 2% salt for 105 seconds had highest quality as evident from
ascorbic acid (7.45 mg/100g), antioxidant activity (38.74%), total phenols (21.67 mg/100g GAE),
total chlorophyll (11.96 mg/l) and chlorophyll a (6.86 mg/l) and b (3.08 mg/l). However, mechanical
drying of nettle leaves resulted in a higher loss of chlorophyll a and b content compared to vacuum
drying. In contrast, the total phenol content and total antioxidant activity was higher in vacuum dried
Stinging nettle leaves compared to cabinet dried leaves. Stinging nettle leaves powder potentially be
used as a cheap natural source of antioxidant and considered safe for human consumption because no
microbial growth was recorded during their accelerated storage period at temperature 37 0C and 47 0C
for different days interval. Hence, it is concluded that when Stinging nettle leaves processed by using
appropriate method then it helps to retain the entire quality characteristics with excellent nutritional
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