Food for the Eyes: The Psychology of Food Color and the Visual Cues of Vegetable Nutrition

An experiment was once conducted where participants were asked to identify fruit juices with the aromas of several fruits, such as citrus and pineapple, without any labeling. The results showed that all participants correctly identified the juices containing citrus flavoring because of their citrus color, while less than half correctly identified the colorless juices. Furthermore, only one-fifth of the participants correctly identified a juice containing both citrus flavoring and a purple food coloring reminiscent of grapes.

In daily life, people feel a sour taste and salivate at the mere sight of bayberries. This is a physiological and psychological response caused by visual conditioned reflexes. Although consumers have gained some knowledge about food additives such as food dyes and thus avoid them, they still tend to choose visually appealing and delicious foods. This is also why the food industry continues to use food dyes extensively. Bright red tomatoes and fresh leafy green vegetables are immediately recognizable as delicious. Moreover, the color of vegetables is also a nutritional indicator.

The red, orange, and yellow pigments found in vegetables and other plants are all carotenoids, primarily functioning as vitamin A. Carotene, one type of carotenoid, is the pigment that gives carrots their color. The depth of a carrot's color reflects its carotene content. When leafy green vegetables are placed in sunlight, their green color fades and they turn yellow. This is because the green chlorophyll is broken down by light into colorless substances, thus making the yellow color of the carotenoids that were already present visible.

Spinach, lettuce, parsley, perilla, rapeseed, and garland chrysanthemum are among the leafy green vegetables that mostly contain carotenoids, which have vitamin A-like effects. Nutritionally speaking, vegetables containing an average of 0.6 mg or more of carotenoids per 100 grams are considered leafy green vegetables. After being absorbed by the body, vitamin A is stored in the liver. Vitamin A combines with protein to form rhodopsin, the substance in the eye that senses violet-red light. A deficiency in vitamin A can lead to night blindness, difficulty seeing in the dark, insufficient tear production causing dry eyes, rough skin and mucous membranes, and increased susceptibility to colds.

In addition, vegetables contain vitamin C, calcium, and other minerals, as well as dietary fiber, considered the sixth nutrient. Bright red apples stimulate appetite. The red color of apples comes from anthocyanins. Ultraviolet and infrared rays promote the formation of this pigment. Using this principle, by partially blocking sunlight from reaching the apple, words or patterns can be displayed on it. Such apples are already available in the market. When eating food, taste is very important. It's not just about whether it tastes good or not; taste also has a significant impact on digestion.

First, your saliva will start to flow when you see food, smell its aroma, or even just imagine its delicious taste. Once the food is in your mouth, if the taste and texture are appealing, you'll produce even more saliva. The food softens in your mouth as it's moistened by the saliva. Next, the salivary amylase and maltase in the saliva break down starch into maltose. At this time, gastric juices also begin to be secreted in large quantities, accounting for about 45% of the total gastric juice secretion. This gastric juice also contains a particularly high amount of pepsin, a protein-degrading enzyme.

At the same time, the pancreas rapidly secretes pancreatic juice. Pancreatic juice, containing various digestive enzymes, begins to be secreted approximately 1-2 minutes after food is ingested. Bile secretion is also stimulated after eating. This stage of digestive juice secretion is called neurogenic secretion, which occurs when the food is perceived as delicious. Subsequently, food enters the stomach, stimulating the pyloric mucosa to secrete a hormone called gastrin. This gastrin travels through the bloodstream to the gastric mucosa, stimulating gastric juice-secreting cells to begin secreting gastric juice, which is rich in gastric acid.

Under normal circumstances, gastric acid is strongly acidic with a pH of 1.6–1.8. This is due to the hydrochloric acid in gastric acid. The strong acidity of gastric juice plays a crucial role in killing microorganisms that enter the stomach along with food. If the food entering the stomach is mainly starchy, less gastrin is secreted; however, if it is mainly meat, gastrin secretion increases. Clearly, the stomach can also "sense" the type of food and whether it is palatable. This stage of digestive juice secretion is called gastric secretion. The amount of gastric juice secreted at this stage is similar to that secreted by the brain, accounting for about 45% of the total gastric juice secretion.