1. Why are our foods decreasing in the nutrient content?
In recent decades, modern agriculture has been evolving towards monoculture in order to increase crop yields. This boost in food production has been mainly due to the use of pesticides, herbicides and fertilizers, development of large-scale agricultural machinery, tillage and GMOs. Although modern agriculture successfully meets the growing demand for food by the worlds’ population for now, it has been destroying soil and plant health in the long run, which also results in declining nutrient content of crops. There are two main causes why modern agriculture decreases the nutrient content of our food.
1. “Genetic Dilution Effect”. Commercial plant breeders keen on developing “improved” species which grow bigger crops and give higher yields so that farmers can increase their profits. Since 80-90% of the dry weight yield of vegetables and fruits is usually carbohydrates, “improved” species are actually selecting crops with high carbohydrates with no assurance that other nutrients will also increase in proportion to yield . Hence, commercial farm practices genetically dilute nutrient content of bigger vegetables and fruits.
2. “Environmental Dilution Effect”. Commercial agriculture uses a high rate of fertilizer to increase crop yields. However, if the crops are fertilized (e.g. phosphorus) beyond a certain level, the crops would contain more phosphorus, but the other minerals and vitamins absorption would be inhibited due to antagonism (i.e. decreased availability of other nutrients to plants due to the chemical reaction of certain nutrient.).
Although vegetables and fruits are getting bigger and heavier nowadays due to selective plant breeding and fertilization techniques, their nutrient content does not increase proportionally, or even decline because of dilution effects. Not only do these effects apply to vegetables and fruits, but also to meats, eggs and dairy products. Compared with industrial products, foods from animals raised on pasture are richer in vitamins A, D and E, beta-carotene and other beneficial fatty acids .
 Davis, D. R. (2009, February). Declining Fruit and Vegetable Nutrient Composition: What Is the Evidence?, HortScience horts, 44(1), 15-19. https://doi.org/10.21273/HORTSCI.44.1.15
 Peskett, M. (2017, February 8). It Seems Modern Fruits and Vegetables are Bigger, But No More Nutritious. Retrieved from https://www.growlikegrandad.co.uk/allotment/seems-modern-fruits-vegetables-bigger-no-nutritious.html
 Mother Earth News. (2012, January). The Declining Nutrient Value of Food. Retrieved from https://bionutrient.org/site/news/declining-nutrient-value-food
2. Why are polyphenol and chlorophyll content used as indicators for nutrition and freshness check?
Polyphenols are plant-based nutrients that are generally used for plant defense against ultraviolet radiation (UV) and aggression by pathogens. Research on polyphenols in the human diet has been done in recent decades. The result found that polyphenols exert a protective effect to control chronic diseases, so they are regarded as “lifespan essentials” . Common types of polyphenols include flavonoids in brightly colored vegetables, curcumin in turmeric and lignans in flax seeds, sesame seeds and whole grains. The rise of polyphenols has gradually caught attention in recent years and have become one of the nutritional indicators for plant-based foods.
Chlorophyll is a green pigment found in plant leaves. It is essential in photosynthesis, which allows plants to absorb light energy and convert the energy into sugars (i.e. food for plants). Therefore, chlorophyll plays an important role in plants’ primary metabolism. As leaf chlorophyll will be degraded gradually along with postharvest senescence, chlorophyll content can estimate the harvest time of green leafy vegetables . Thus, high leaf chlorophyll content implies that the vegetables are harvested recently and the freshness is also high. As a result, chlorophyll content of green leafy vegetables can be used as visible parameters for the quality and freshness of vegetables.
 WebMD. (2020, October 26). Healthy Foods High in Polyphenols. Retrieved from https://www.webmd.com/diet/foods-high-in-polyphenols#1
 Guo, Y., Liu, J., Qiu, Y., & Zhao, Y. (2017, December). A Statistical Analysis of the Freshness of Postharvest Leafy Vegetables with Application of Water Based on Chlorophyll Fluorescence Measurement. Information Processing in Agriculture, 4(4), 269-274. https://doi.org/10.1016/j.inpa.2017.08.001