What is Fruit Flavor, and How to Measure it

• Fruit flavor is the interaction of taste and aroma.
• Taste is determined by sugars and acids and aroma by distinctive combinations of hundreds of volatile compounds.
• New non-destructive, precise, and objective flavor estimation possibilities will increase the use of this quality parameter in the supply chain and research.

Interest in fruit flavor is resurgent due to consumer pressure for better and fresher flavors. Difficulty estimating flavor has hampered flavor development, but new technology can change that. Learn more about fruit flavor and how we can measure it.

What is Fruit Flavor?

Fruit flavor is the interaction of aroma and taste, both major fruit quality attributes. Aroma refers to the smell of fruits, while the taste is the balance between sweetness and sourness. Aroma is a retronasal olfaction perceived by the nose; the taste is the orthonasal olfaction perception in the mouth.

Consumers evaluate fruits initially by color and appearance in terms of size, shape, and gloss. After eating, the flavor and texture determine consumer satisfaction and make them go for repeat buys.

The fruit’s flavor is referred to as the ‘modern concept of quality‘ However, the flavor is not a new concept. Since flavor results from the interaction of many chemicals, this quality parameter is more challenging to manipulate to meet consumer satisfaction. Therefore, it has been neglected in the recent past. However, consumer demand for flavor is attracting more attention. Producers are aiming to improve flavor to ensure assured sales and profitability.

It isn’t just good flavors that are important, “off-flavors,” such as rancid, oxidized, cardboard, or wet dog, produced by enzymes acting on lipids must also be identified to cull spoilt fruits.

What gives Fruits Flavor?

Aroma and taste result from chemicals, such as sugars, organic acids, amino acids, vitamins, phenols, volatile compounds, minerals, and salts. This section will break down and cover what gives fruits such unique flavors.

Taste

Sugars and acids determine taste, but their importance depends on the fruit.

Sugars make fruits sweet. The sugars ranked in their ability to make fruits sweet are fructose, followed by sucrose and glucose. The sweetness will depend on the concentrations of these sugars in the fruit.

The organic acids that make fruits sour are malic, citric, and tartaric. Citric acid is the most sour, and tartaric acid is the least sour. The organic acid can be specific to fruits. For example, citric acid is found in citric fruits, malic acid in apples, and tartaric acid in grapes. Fruits like melons and bananas have little acids. Minerals and salts combine acids and moderate sourness.

Figure 1. Grape berry flavor compounds are in the skin, Gonçalves et al. 2018. (Image credits: https://www.intechopen.com/chapters/61698)

Aroma

The aroma fraction can influence consumers’ perception of taste.

Volatile compounds produced during fruit ripening are responsible for producing aroma. The volatile compounds vary in different fruits but are alcohols, aldehydes, ketones, esters, lactones, and terpenoids. They are made from phytonutrients like lipids, amino acids, and carbohydrates.

Volatile compounds are usually found in the skin of the fruits and not the flesh; see Figure 1.

Table 1: Key volatile compounds in some common fruits, Gonçalves et al. 2018. (Image credits: https://www.intechopen.com/chapters/61698)

The number and type of volatile chemicals involved will vary with each species (see Table 1). For example, isoamyl acetate and a few other compounds are responsible for the aroma of banana flavor. The aroma of apples and oranges results from more than 300 volatile compounds each.

The combination of the volatile compounds produces the distinctive aroma of each fruit or cultivar. As the fruit ripens, the volatile compounds profile changes. For example, immature apples have green notes due to aldehydes and alcohol, while ripe apples have esters.

Besides the chemicals, flavor is also influenced by cultivars or genetics, soil and climatic factors, farm management, postharvest handling, treatments, use of an edible coating, and type of packaging, see Figure 2. Attempts to improve flavor should do so without compromising on other quality traits.

Figure 2: “Factors affecting flavor formation in horticultural crops,” Gonçalves et al. 2018.    (Image credits: https://www.intechopen.com/chapters/61698)

Measuring Flavor

A fruit flavor is measured for evaluating and selecting fruits for maturity and ripeness at harvest and during market sales. Flavor changes during fruit development and ripening in the preharvest and postharvest stages during storage. Therefore, it has to be monitored periodically.

The flavor is measured through an array of subjective and objective methods.

Traditional Methods

Traditionally, flavor was estimated using a panel of trained professionals or consumers. They scored fruits on all flavor attributes of sweetness, sourness, mealiness, and flavor intensity. Panel descriptions can be subjective even when professionals are involved. Sweetness, firmness, and aroma were rated essential to evaluating flavor, but not sourness.

Taste can be evaluated by estimating total soluble solids (TSS), titratable acidity (TA), the ratio of TSS and TA (TSS/TA), and firmness. There are several different methods to measure TSS, acidity, and firmness.

• The refractometer can measure TSS as Brix.
• The penetrometer is used for firmness.
• Titration by neutralizing the acid in a known sample quantity with a standard base gives a simple estimation without identifying the acid.

Though these methods provide accurate and objective estimations, they require destructive sampling and are time-consuming.

Sensor-Based Estimation

Recent developments enable sensors to employ non-destructive, objective, qualitative, and quantitative assessments of all flavor attributes.

Near Infrared (NIR) Spectroscopy-based devices use sensors to collect the spectrum produced by directing a beam of NIR light on the fruit and analyzing them by chemometrics. Small and portable F-750 and F-751 Felix Produce Quality Meters are an example of NIR spectroscopy-based instruments that can provide precise measurement in real-time. The quality meters measure TSS, titrable acidity, and external and internal color.

Electronic nose (E-nose) devices have many sensors that evaluate all the volatile compounds in a sample by converting the electronic outputs and combining them to give an Electronic Aroma Signature Pattern specific to the gas mix in the fruit. The E-nose evaluates the volatiles and their concentrations to define the aroma.

Both these devices avoid reliance on variable and subjective estimations by human graders.

Flavor Measurement Applications

These non-destructive sensor-based instruments provide new means for characterizing fruit flavor. It is now possible to track flavor development in the same fruit over time to find and manipulate growing or postharvest conditions.

• Scientists can use these precision tools to develop new fruit cultivars.
• Growers can use them to fix harvest time.
• Flavor detection can be used for grading and sorting fruits.
• Suppliers and distributors can monitor fruit quality during transportation and storage.
• Flavor estimations can guide final fruit selection by retailers and suppliers.

Flavor and Nutritional Value go hand-in-hand.

As new technology solves the challenges of measuring and evaluating flavor, emphasis on this quality parameter can be expected to grow. Since flavor is also associated with phytochemicals that make fruits healthy, consumers’ benefits will extend beyond an enhanced sensory experience of eating flavorful fruits. For producers, it means more sales and profits.

Sources

Alavoine, F., Crochon, M. and Bouillon, C. (1990). Practical methods to estimate taste quality of fruit: how to tell it to the consumer. Acta Hortic. 259, 61-68. DOI: 10.17660/ActaHortic.1990.259.4. https://doi.org/10.17660/ActaHortic.1990.259.4

Baietto, M., & Wilson, A. D. (2015). Electronic-nose applications for fruit identification, ripeness and quality grading. Sensors (Basel, Switzerland), 15(1), 899–931. https://doi.org/10.3390/s150100899

Barrett, D. M., Beaulieu, J. C., & Shewfelt, R. (2010). Color, flavor, texture, and nutritional quality of fresh-cut fruits and vegetables: Desirable levels, instrumental and sensory measurement, and the effects of processing. Critical Reviews in Food Science and Nutrition, 50(5), 369–389. https://doi.org/10.1080/10408391003626322

Fan, Z., Hasing, T., Johnson, T.S. et al. Strawberry sweetness and consumer preference are enhanced by specific volatile compounds. Hortic Res 8, 66 (2021). https://doi.org/10.1038/s41438-021-00502-5

Gonçalves, B., Oliveira, I., Bacelar, E., et al. (2018). Aromas and Flavours of Fruits. InTech. doi: 10.5772/intechopen.76231

Verkerke, W., Janse, J. and Kersten, M. (1998). Instrumental measurement and modelling of tomato fruit taste. Acta Hortic. 456, 199-206. DOI: 10.17660/ActaHortic.1998.456.22.https://doi.org/10.17660/ActaHortic.1998.456.22