Effects of Domestic Freezing Temperature (-20˚C) and Blanching on the Functional Properties and Constituents of Three Common Culinary Herbs of Lamiaceae Family

Iheozor-Ejiofor, Pamela Annmary MMA (2020) Effects of Domestic Freezing Temperature (-20˚C) and Blanching on the Functional Properties and Constituents of Three Common Culinary Herbs of Lamiaceae Family. PhD thesis, University of Lincoln.

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Effects of Domestic Freezing Temperature (-20˚C) and Blanching on the Functional Properties and Constituents of Three Common Culinary Herbs of Lamiaceae Family
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Abstract

The effects of blanching prior to freezing on the functional constituents (ascorbic acid, selenium, phytic acid and phenolic content) and properties (total antioxidant activity, enzyme inhibition activity and prebiotic functions) of 3 well known Lamiceae herbs (mint/Mentha piperita, thyme/Thymus vulgaris and basil/Ocmium basicilla) were investigated. Comparisons were made between herbs and across different treatments (fresh, un-blanched frozen (-20˚C) and blanched frozen). Due to the complexity of antioxidant and phenolic compounds/components of plants, extracts for total phenolics and antioxidant activities were made in methanol and water.

Generally, among all assayed herbs, mint showed superiority compared to other herbs in terms of functional constituents and properties. However, results of antioxidant capacity/content (DPPH, ORAC, FRAP and CUPRAC) and TPC varied inconsistently across herbs, treatments and assays.

Results also showed that frozen herbs have lower selenium, ascorbic (total, and reduced) and phytic acid content compared to fresh herbs. Furthermore, results of ascorbic acid content showed a significantly lower dehydroascorbic acid (DHA) content in frozen herbs than fresh herbs.

Results of enzyme inhibition showed a moderate to very low α-amylase inhibition ability by all herbs which further reduced on freezing and blanching. Furthermore, compared to other herbs, mint showed the highest α-glucosidase inhibition which reduced on freezing and blanching. Lineweaver-Burke plot showed that fresh and un-balnched frozen mint displayed un-competetive mode of inhibition while blanched frozen mint showed mixed inhibition. Freezing tended to improve the α-glucosidase inhibition effects of thyme and basil which was not evident in fresh extracts. None of the herbs showed inhibitory effects against ACE.

All herbs showed significant prebiotic effects on probiotic bacteria L. rhamnosus and B.bifidum. However, effects of freezing and blanching varied inconsistently among herbs

Results of the functional properties correlated with individual phenolic acid content of herbs. This therefore shows that the product of the hydrolysis of these individual phenolic compounds play significant role in the functional properties of the assayed herbs.

The findings from this research have therefore shown that freezing (blanching or without blanching) can positively or negatively affect the assayed functional constituents and properties of assayed lamiceae herbs. However, in some instances, there is no difference between the functional constituents of fresh and frozen (un-blanched and blanched)

Divisions:College of Science > School of Life Sciences
ID Code:46815
Deposited On:04 Oct 2021 12:54

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