Increasing of bioactive compounds in Mentha cordifolia Opiz., kitchen mint via ZnSO4 biofortification during plantation
Background: Plant growth generally requires both macronutrients and micronutrients. One of the most important micronutrients for plants is zinc. Zinc is an essential nutrient for every life form, including plants. In particular, zinc aids enzymatic processes and many biochemical reactions. When plants receive an inadequate amount of zinc, it leads to the loss of imperative biochemical reactions, which is also related to inhibition of plant growth. Therefore, the yield of the plant is relatively low. Interestingly, some scientific evidence have demonstrated a positive relation between zinc intake and the amount of essential oil and yield of plants. Mentha cordifolia Opiz., kitchen mint, is one of the top seven vegetables consumed in Thailand. The increase of some essential minerals in plants or biofortification during plantation has resulted in the increase of essential oils and chlorophyll. The bioactive compounds of essential oil provide antibacterial benefits. Additionally, chlorophyll can be utilized for against sinusitis, purifying the blood, and cleansing of toxins from intestines.
Objective: Our study aimed to evaluate the effects of fortifying zinc into plantation soil on growth characteristics, essential oil droplets, and overall quality of Mentha cordifolia Opiz.
Methods: Mentha cordifolia Opiz were planted in soil fortified with ZnSO4 at 0 (control), 100, and 200 ppm and grown for 3 months. During the growth period, physical characteristics were observed. After harvesting, proximate analyses were conducted as well as determination of minerals, and chlorophyll content, were conducted. Microbiological and sensory tests were also performed.
Results: The increase of growth characteristics correlated with the increase of zinc concentration. The sizes of mint leaves were larger, the stalks were plumper, and the length of the roots were longer—although not significantly different—and the production of essential oil significantly increased. The approximate composition contents including protein, fat, ash, and fiber of plants grown in fortified ZnSO4 soil, increased when compared to the control. The leaves grown from the soil containing the 100 ppm ZnSO4 treatment possessed the highest chlorophyll content, related to lowest in a* value. Overall, the kitchen mint fortified with 100 ppm ZnSO4 seemed to be the most tolerable sample when analyzed for color and sensory attributes. Furthermore, it was discovered that 200 ppm ZnSO4 treatment demonstrated the highest production of essential oil and lowest number of microorganisms.
Conclusion: In conclusion, soil fortified with ZnSO4 at 100 ppm during seeding increased greenness, chlorophyll content, and consumer acceptability of the mint leaves. Darker and larger oil droplets were found in the mint leaves obtained from plants grown in soil fortified with 200 ppm ZnSO4.
Keywords: Fortification, Growth characteristics, Zinc deficiency, kitchen mint, oil drop
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