Why is Fruit Flavour Important?
The flavour of the fruit is very closely linked with the consumer’s preference and continued consumption of any given fruit variety and should be strongly considered. Meeting consumer expectations for flavour of specific fruit, not only causes consumers to buy more fruit, but it allows growers to increase their profitability. Consumers are willing to pay a higher price for distinctly flavourful varieties that are going to enhance their experience consuming fresh fruit.
There is nothing more disappointing for consumers than finding the perfect apple or peach from the grocery store — a beautiful red color, no bruises, a firm texture — but when taking the first bite, the flavour is boring, flat, and is overall a disappointment. Once a consumer has purchased a fruit with little or poor flavour, they are inclined to not buy those fruit again and/or move on to a different grower or a different fruit all together. Producing fruit with complex and delicious flavour is extremely important to the consumer’s enjoyment of their eating experience.
What is Fruit Flavour?
Flavour is described as the interaction between taste and aroma. Taste relates to the ratios and intensities of non-volatile compounds, specifically sugars, and acids. Sugars and acids are detected by five classes of receptors in the tongue – sweet, sour, salty, bitter, and umami (protein taste, represented by glutamate). Volatile compounds, which create the aromas of fruit, are detected by over 650 types of olfactory nerve endings found in the nose.
The sweetness of a fruit is influenced by the quantity and composition of sugars. Higher contents of sugar in the fruit increases the sweetness of the fruit. Additionally, different forms of sugar affect the sweetness of the fruit. In fruit such as apples, peaches, and plums, the main sugars present are sorbitol, sucrose, fructose, and glucose. Each of these sugars have a different degree of sweetness. Fructose has 1.7 times the sweetness of sucrose, while glucose and sorbitol only have 0.8 and 0.6, respectively. For example, if one variety has higher contents of fructose and another variety has higher glucose, the former will taste sweeter.
The acidity of a fruit is influenced by the content and composition of organic acids, and the amount of each type of acid found in each fruit. For example, the dominant acid in apples, peaches, and plums is malic acid.
The balance between the sweetness and acidity of fruit based on the quantity and composition of their sugars and acids is important for developing a complex and interesting taste that will enhance fruit flavour.
Another key component of flavour is aroma. Fruit aroma is influenced by the quantity and composition of volatile compounds. The volatiles that are well-known to affect fruit flavour include esters (fruity aroma), alcohols (fruity or earthy aroma), aldehydes (slightly grassy and bitter aroma), lactones (peach-like aroma), and terpenoids (scented oils aroma). Studies have shown that the flavour intensity of a fruit can be correlated with the quantity and composition of volatiles present. For example, strawberries that presented higher levels of certain key volatiles were perceived as sweeter and highly preferred by consumers, as compared to other strawberry varieties lacking these volatiles.
How is Fruit Flavour Measured?
Fruit flavour can be measured instrumentally as well as through the use of sensory science. Sensory science is a multi-disciplinary field that uses scientific measurements to interpret the human response to the senses of sight, smell, taste, touch, and hearing. This form of science is able to link the product to the person in a direct way.
Instrumentally, sugar content of the fruit is determined by measuring the soluble solid content using a portable refractometer. A refractometer measures how light is bent as it passes through a sample, which is correlated to a specific percentage of sugar in the fruit, and thus is related to fruit sweetness. Titration measures the content of the dominant acid present in the fruit and can also be measured and calculated using portable acidity/pH meters.
Aroma volatiles are challenging to measure with portable instruments. They are quantified by using Gas Chromatography – Mass Spectroscopy (GC-MS), a lab-based technique which helps to separate and identify compounds in their gaseous forms based on their masses.
To correlate these instrumental measurements to consumer perception, two major methods of sensory evaluation are used: consumer testing and descriptive analysis. Consumer testing includes subjective data about the preferences of a large group of untrained tasters (usually more than 100 panelists), while descriptive analysis includes questionnaires for a panel of 8-12 trained tasters who are able to rate specific attributes related to fruit quality.
What Factours Affect Flavor Development?
A key factor for determining fruit flavour lays in the genetic background of the variety that was chosen. When determining which variety to establish, it is important to choose varieties that were bred for flavour as one of its priorities. Additionally, the choice of rootstock, for fruit such as apples, can influence fruit flavour potential. Studies have shown that particular rootstocks can affect the levels of organic acids and sugar content found in the same variety of apple.
Environmental factors also play a hugely important role in affecting the flavour of the fruit and strongly interact with the genetic background. Although often times these factors cannot be controlled, they must be taken into account when aiming to improve the flavour of the fruit that are being produced. The major environmental factors affecting fruit flavour development include temperature, relative humidity, and sunlight during the growing season.
A good practice before establishing a new orchard is to conduct small variety trials to evaluate which varieties are capable of developing flavour under the specific environmental conditions. As there is strong interaction between varieties and their growing environment, a variety that is successful in one area may not be as successful in another region.
Preharvest Factors, Orchard Management, and Cultural Practices
Fruit flavour can be affected by different orchard management practices, such as planting density, tree structure, irrigation regime, light manipulation, crop load, nutrition, and pest control methods.
Practices that increase the amount of sunlight reaching the fruit, such as pruning or the use of reflective groundcovers, have been shown to increase flavour development as well as colour.
Crop load management is another important factor affecting fruit flavour development. In a study done on apples, trees with lower crop loads were found to have fruit with increased flavour development. This was mainly due to higher levels of aroma volatiles and sugars in the apple fruit with lower crop load. Many times, trying to aim for the highest yield will play against flavour development.
Irrigation management can also have an effect on fruit flavour. It is important to maintain balanced irrigation levels in the orchards. Excess irrigation will decrease the overall flavour produced during the fruit growth. Irrigating in intervals to avoid inducing stress on the tree is good practice and will positively impact fruit flavour development.
Concerning nutrition, excessive levels of nitrogen will decrease the “fruity” aromas that are developed in the fruit, while increasing the “green” and “grassy” aromas. Many studies have shown that moderate nitrogen supply for the tree increased fruit flavour, but an excessive amount actually deteriorates fruit flavour.
Fruit Maturity at Harvest
Harvesting practices and the maturity of the fruit at harvest is an often-forgotten key factor in maintaining fruit flavour. Fruit produced for wholesale distribution typically tends to be harvested before fully ripe in order to ensure that the fruit can be transported easily without being damaged. Unfortunately, in this case the fruit’s flavour is likely not completely developed. On the other hand, if fruit are harvested over-mature, there is an increase in the “fermented” flavour, which is disliked by consumers.
Harvesting fruit at the correct time is a ‘balancing act’ between great flavour, overall quality, and shelf-life capacity. Favouring one of these factors over others may affect the marketability of the fruit, so it is of key importance to harvest fruit at the correct time.