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 (2020) Effects of domestic freezing temperature (-20˚C) and blanching on the functional properties and constituents of three common culinary herbs of Lamiaceae family. MRes 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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Item Type:Thesis (MRes)
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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).

Keywords:freezing, food preservation, Lamiceae
Subjects:D Veterinary Sciences, Agriculture and related subjects > D690 Food studies not elsewhere classified
Divisions:College of Science > National Centre for Food Manufacturing
ID Code:48486
Deposited On:08 Mar 2022 15:18

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