Evaluation of Different Storage Conditions on the Chemical, Physical Properties and Anti-Microbial Activity of Garlic, Onion and Garlic-Onion Paste

Chan, Jun Xian (2021) Evaluation of Different Storage Conditions on the Chemical, Physical Properties and Anti-Microbial Activity of Garlic, Onion and Garlic-Onion Paste. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Onion and garlic are the frequently used condiments in foods. Both plants are known to rich in phytochemical compounds that exhibit prominent therapeutic effects. This study was conducted to evaluate the physical (pH, color), chemical (Total phenolic content (TPC) , Total flavonoid content (TFC)) and antimicrobial properties changes of garlic, onion and garlic-onion paste at different storage conditions (room temperature under light, room temperature in dark, cold temperature under light and cold temperature in dark condition). Besides, a knowledge survey was also conducted to evaluate the general knowledge of the public toward the benefits of garlic and onion, and the effects of storage conditions on their health value. pH and color of the paste was determined using a pH meter and colorimeter respectively. TPC and TFC of the paste were estimated by using Folin-Ciocalteu assay and aluminium chloride assay, respectively. The antimicrobial activity against Escherichia coli, Staphylococcus aureus and Lactobacillus casei was evaluated using disc diffusion method. Result of the experiment proved that pH, color, TPC and TFC of garlic and onion were significantly affected by their storage conditions. Storage temperature was found to be more influential on the physical and chemical properties of both garlic and onion than the light effect. The garlic paste stored at room temperature in light experienced the highest extent of color change -ΔE of 10.81. pH of all samples was generally dropped upon storage. However, pH drop was less when stored in cold. TPC in garlic paste increased upon storage while TPC in onion paste reduced upon storage. Due to the dominant effects from garlic, TPC of garlic-onion paste was also increased upon storage. Both storage temperature and lighting affect stability of flavonoids and hence TFC in garlic, onion and garlic-onion paste. However, antimicrobial activities of all pastes were declined significantly under all storage conditions. The highest antimicrobial activity was observed in the fresh garlic paste against S. aureus. Antimicrobial activity of pastes that were stored under cold temperature was found decreased while the pastes stored at room temperature has lost its antimicrobial activity. The findings of the survey show that the majority agreed that anti-microbial activity of garlic and onion will be affected by its storage condition. Majority of the respondents has sufficient knowledge regarding the topic investigated.