The Chemistry of Ripening and Flavor Development in Fruits and Vegetables

The ripening process in fruits and vegetables involves complex chemical transformations that significantly influence their taste, texture, and overall quality. A key change during ripening is the increase in sugars and decrease in acids, which enhances sweetness—a desirable trait in many fruits like apples, bananas, and mangoes. However, this transformation varies across crops and is not universally beneficial.

In some cases, sweetness is undesirable. For instance, in sweet corn, ripening involves the conversion of sugars into starch. This reduces sweetness, diminishing its appeal. To retain sweetness, sweet corn is often harvested at a specific stage, known as the milk stage, before excessive starch accumulation occurs.

In tomatoes, flavor complexity arises from the balance between sugars and acids, rather than sweetness alone. Both components are essential in delivering the characteristic tangy and savory taste preferred by consumers. Breeding efforts often aim to optimize this balance, enhancing both sweetness and acidity for superior flavor profiles.

Conversely, the presence of sugars in certain vegetables, such as potatoes, can cause problems. During frying, these sugars undergo Maillard reactions with amino acids, resulting in browning and the formation of compounds that affect both color and flavor. This is particularly problematic in the production of chips and French fries, where uniform golden-brown hues are desirable.

Bitterness and astringency are other important flavor attributes in fruits and vegetables. Citrus fruits, for example, contain bitter compounds like naringin and limonin, which can be off-putting at high concentrations. Similarly, tannins in fruits like persimmons and unripe bananas impart astringency, which creates a dry, puckering sensation in the mouth. These traits often diminish as fruits ripen, improving palatability.

Recent advancements in post-harvest technology and genetic engineering aim to fine-tune the ripening process. Controlled storage conditions, such as modified atmosphere packaging, help regulate sugar and acid levels, extending shelf life while maintaining optimal flavor. Additionally, scientists are exploring gene-editing techniques to enhance specific traits, such as reducing undesirable bitterness or starch conversion.

In conclusion, the ripening process plays a crucial role in determining the sensory qualities of fruits and vegetables. By understanding and managing these chemical changes, producers can deliver high-quality products tailored to consumer preferences.
The Chemistry of Ripening and Flavor Development in Fruits and Vegetables

Taste of umami

In 1908, Dr. Ikeda from Imperial University of Tokyo proposed umami as a distinct taste recognizable in “dashi” which is Japanese stock flavored with kelp and dried bonito flakes.

Beyond the four better known tastes of salty, sweet, bitter, and sour, umami finds its place as the fifth basic taste evoking savory, full-bodied, and meaty flavor sensations. It is best described as a savory or “meaty” flavor.

Umami is an integral part of savory contributing to the taste dimension along with salty. There is a synergy observed between salt and umami taste (Halpern, 2000), meaning that one can reduce salt by umami compounds (and vice versa). However, equally important is the savory aroma to obtain a full savoury perception.

In cooking generally, the effect of adding umami compounds is an increase in savoriness, richness and an almost tactile mouth-filling quality. Mostly, this is achieved by the addition of common ingredients in soups, sauces and stews such as glutamate-rich vegetables and meats.

Umami is the taste imparted by a number of substances. These include glutamate, a salt of glutamic acid, specific ribonucleotides, and glutamate salts including monosodium glutamate (MSG), potassium glutamate, and calcium glutamate among others.
Taste of umami

Taste of sweetness

Sweet, sour, bitter and astringent are the taste attributes of plant products. Sweetness is a property of organic acids. The primary functions of sugar in food products are to provide sweetness and energy.

Sugar has a uniquely clean sweetness that is entirely free from off-taste or aftertaste. Ripeness and maturity are the key factors that influence the taste of a fruit. Fruit ripening is a complex process influenced by several factors. The changes in composition of sugars and organic acids and volatile compounds during ripening process play a key role in flavor development and can affect the chemical and sensory characteristics (e.g., pH, total acidity, microbial stability, sweetness) of fruit.

Tasting something sweet leads to the activation of pleasure-generating brain circuitry. Subjective factors such as appearance and colour can also affect the sensation of taste. In order for a substance to taste sweet, it must be water-soluble and its concentration must exceed the taste threshold. In the context of food, sweeteners are often present in concentrations well above the threshold value.

Sweetness in many fruit and vegetables is a desirable attribute that is often governed, in part, by sugar concentration. Soluble sugars, mostly comprised of glucose, fructose and sucrose, may be determined using refractometry or colorimetry. High performance liquid chromatography (HPLC) is the mostly used technique for analysis of individual compounds.
Taste of sweetness

Taste of spoiled food

To the public, off-tastes and smells in food are probably the least noticeable consequence of microbial spoilage, depending of the perspicacity of the tasters and their familiarity with what the food should normally taste like.

The tastes of spoiled foods range from loss of good characteristic taste to the development of objectionable tastes.

Thus, when a pear or an orange spoil, the sweet characteristics tastes of either is lost, and when milk spoils, it develops an acidic taste, sometimes also bitter. Spoiled food can also make people sick if they eat it.

The feel of spoiled foods reflects the spoilage in different ways, depending on the type of food and the microbe involved in the spoilage, so some spoiled foods feels slimy while others may feel mushy.

Spoiled foods is usually produced by bacteria called pseudomonas and colophons that feast upon poultry, red meats, fish and cheese and thereby impart to these foods the typical off-odor, taste, color and feel with which every homemaker familiar.

In theory, microbial growth and metabolism can influence the flavour and smell of food in one of two ways; ether by removal of flavorsome food components; or by production of off-flavors or off-odors.
Taste of spoiled food 

Astringent taste

Taste indicate the main impact of foods on human sense. The six taste are sweet, salty, sour, pungent, bitter and astringent. The taste of the food is determined by its chemical composition.

Astringency is defined by the tactile sensation of dryness and roughness throughout the mouth. It is the complex of sensations due to shrinking, drawing or puckering of the epithelium as a result of exposure to substances such as alums or polyphenols.

This sensation is because of the presence of tannins. These can tightens mucous membranes, contract tissues and decrease inflammation.

Foods with astringent taste tend to be more alkaline. Very few foods are predominantly astringent. Pomegranates, cranberries, teas, red wine and some unripe fruits such as mangoes and apples are examples of more astringent foods.

Astringency is created in wine through the presence of tannins. Astringent is more often a secondary taste to sweet, such as meats. Most beans and grains are primarily sweet with a secondary taste of astringency.
Astringent taste

Food taste

Taste is detected by the taste buds’ connection to the brain via nerve cells, which signal the sensation of sour, salt, sweet, bitter and savory.

Taste buds themselves are clusters of between 50 and 150 taste receptor cells. They are globular with an opening called a taste pore at the top. Each of them waits for food molecules of a certain type to enter the taste bud.

People vary in their sensitivity to different taste. Sensitivity depends on the length of time allowed to taste a substance.

Sweet and salt tastes are detected quickly in less than a second, because they are detected primarily on the tip of the tongue; in addition, they are usually very soluble compounds; whereas bitter taste are detected mainly by taste buds at the back of the tongue.

Sensitivity to a particular taste also depends on the concentrations of the substance for the taste.

Another factor affecting taste is the temperature of food. A food or beverage temperatures go below 20° C or above 30° C, it becomes harder to distinguish their taste accurately.

Other factors influencing taste include the color of the food; the time of day it is eaten and the age, gender and degree of hunger of the taster.
Food taste

Pungent taste

There are six primary taste sensations-sweet, sour, salty, bitter, astringent and pungent. Being the hottest of the six taste, the pungent taste is very well known for increasing the strength and power of digestion.

Pungent taste are strong, hot, spicy, acrid and biting. Such taste are found in mustard greens, onions, garlic, chili peppers, cayenne, cinnamon, radishes and ginger.

Black pepper contains 3-8% of piperine as the most important pungent substance.

While the pungent principle of capsicum is capsaicin. It show similarity to the compound zingerone, the pungent principle of ginger. In small amounts pungent tastes stimulate the digestion, clear the sinuses, dispel gas from the body.

The taste is warming, increases circulation and promotes sweating. It is purported to help liquefy body fat and to expel it from the body as well as to increase metabolism.

If excess pungent taste, the foods cause a burning sensation and thirst in the throat, a dryness of mouth and lips, intense body heat and gastritis.

Pungent tastes can also burn mouth, make the eyes water, and create excess mucus secretion.
 Pungent taste

The Sense of Taste

The Sense of Taste
In physiological terms, the sense of taste can be describe as the sensations perceive in the mouth when a food and drink is consumed.

This is basically accomplished by chemical interaction of food components with taste sensory tissues in the tongue and other areas in the mouth. Commonly can be called these the “taste buds”.

However, the overall sensory impact experienced when food is tasted involves more than just the actual individual taste sense.

It is often more of a combination of taste with several additional senses – olfactory (smell), visual, touch and sometimes, even sound.

Would freshly squeezed orange juice taste like orange without the aromatic impact of the volatile citrus oils in the peel and the juice itself on sense of smell?

Would it taste like orange if, for some absurd reason, it was deep purple in color?

Would we not think something was wrong if we did not feel and sort of “hear” the small little juice sacs pop in our mouth as we swirl the liquid around our tongues?

Food technologists tend to think in terms of a drink’s “sensory properties” when evaluating it for taste.

These are the different sensory perception factors that impact on our brain: sweetness, sourness, flavor, mouthfeel, color, clarity, etc.

In a carbonated soft drink the gas content or its “fizziness” is a critical factor as well.

In addition to the sensory factors the temperature and presentation of the tested product would also play a significant part in the test results.

Therefore, a “taste test” would not only mean how does it taste but would also refer to a general evaluation of its sensory properties.
The Sense of Taste