Fruit Quality: The Importance of Fruit Textural Characteristics
Why is texture important?
Texture is a key fruit quality component when considering consumer acceptability. Fruit texture is usually perceived first with the sense of touch and then by the sensation experienced when eating it. Most consumers want a crisp, crunchy apple and a peach that is juicy and has a melting texture, meaning it yields to chewing without being mushy. Meeting these texture standards can increase fruit marketability.
Fruit texture, and particularly flesh firmness, is used as an important maturity index, in combination with other quality parameters. For wholesale, fruits will be harvested when the fruit presents a firm texture to allow for easier handling and decreasing bruising. For example, apples that will be stored longer than 3 months should be harvested with firmness of at least 15 lbs. When fruits will be harvested for farmers' markets, fruit firmness should be around ~13-15 lbs.
Measurement of fruit texture
To accurately measure the texture of the fruit, tests can be performed instrumentally or by using human subjects through sensory evaluation.
Instrumental techniques can involve destructive techniques, the most common of which is the puncture test using a handheld penetrometer or a firmness tester. A penetrometer works by measuring the force required to puncture fruit flesh to the point of irreversible damage. Common brands include Effegi firmness tester (Fig. 1) and Magness-Taylor pressure tester. These pressure tester’s use a 7/16-inch diameter plunger for apples and a 5/16-inch plunger for peaches. The process for testing your fruit is as follows: first, remove a patch of skin the size of a quarter. Second, hold fruit against a hard surface and force the plunger into the skin up to the scribed line on the plunger (7.9 mm). Perform this action on both sides of the fruit, compressing the plunger at a consistent speed to get accurate readings.
Sensory techniques can be thought of as the same concept as taking a bite of the fruit and deciding on its quality. Human subjects can be trained on different textural attributes that are then used to describe the product; or a large number of untrained human subjects are asked to gauge preference as consumers of the fruit they are sampling.
What are some of the factors that affect fruit texture?
In peaches, there are big differences in texture when comparing peaches belonging to the non-melting types, melting types, and stony hard classes. Non-melting type peaches retain their firmness and soften slowly so they are best for canning.; while melting type peaches, soften faster as they ripen and are grown to be eaten fresh (Fig. 2).
Stony hard types soften even less than non-melting type and have a crisp texture. Apples can also vary in their texture: Fuji is known to have a soft and crisp texture, whereas Honeycrisp apples are characterized by their crispness, as the name suggests, but also their crunchiness and juiciness.
Orchard crop load management: Thinning and pruning can impact fruit texture through affecting fruit size and sunlight exposure of the fruit. Thinning has also been shown to improve texture characteristics at time of harvest. In a study on Royal Gala apples, fruit firmness was positively correlated with fruit size, meaning larger fruits were slightly firmer at harvest than smaller fruits. Pruning is also key for fruit texture characteristics. Through correct pruning practices growers can assure, among others, that the canopy optimizes light distribution to all fruit on the tree. Incorrect pruning can lead to fruit shading, leading to underripe fruit that is smaller and with a hard, undesirable texture.
Orchard Nutritional management: Overall avoiding nutrient imbalances is crucial for maintaining fruit optimum texture characteristics. For example, fruit from trees that are nitrogen deficient will usually be smaller with firmer texture. Excess nitrogen on the other hand leads to fruit that loses firmness faster, decreasing its storability potential. A key player in fruit texture characteristics is calcium. Inadequate calcium levels can lead to premature softening, thus supplementing fruit with calcium sprays is recommended for a high-quality texture, and longer storage potential. Potassium deficiency also leads to texture changes as the trees will produce small, poorly colored fruit that may not ripen, thus, leaving the fruit hard and inedible. Boron is another important nutrient to consider as a lack of boron can relate to development of fruit with a mealy texture.
Irrigation management: A crop experiencing drought from lack of rain or due to irrigation management may have fruit with low turgor pressure which can lead to a premature softening of the texture. Whereas a crop that receives excessive water either from irrigation or rain may end up cracking as a result of cells bursting.
Light is one of the most important factors to achieve optimal fruit quality, thus another reason why pruning and training are such important practices. By ensuring all fruit on a tree receive proper, uniform sunlight the desired texture will be achieved in combination with other practices.
Temperature during fruit development also plays an important role as it has been shown that peach and apple orchards that experience hotter than average temperatures in spring experience increased fruit growth rate early in development. The trees are unable to keep up with this increased rate and ultimately end up with smaller, firmer fruit that will not soften. Hotter than average temperatures in summer and fall will also advance maturity, which can lead to a premature softening of the apples after harvest if not properly treated.
Rainfall and humidity are also important factors to consider. In the Mid-Atlantic, the occurrence of rainfall during the growing and ripening season can lead to trees being oversaturated with water which can consequently lead to fruit splitting/ cracking (Fig. 3). Contrarily, it has been shown that fruit experiencing drought stress undergo chemical and physical changes to their cells that end up decreasing fruit firmness.
Preharvest fruit maturity management
Ripening regulation is highly associated with the production of the plant hormone ethylene. As ethylene production increases, the softer the fruit becomes. This can increase fruit drop from the tree, as well as make fruits more susceptible to handling (bruises, injuries, disease exposure) and decrease storability.
Preharvest plant growth regulators are available to growers who want to control ripening. The application of these products will also impact fruit textural characteristics. Chemistries such as Ethephon (Ethrel®, Bayer Crop Science; MotivateTM, Fine Americas; Ethephon 2, Arysta LifeScience North America, LLC), which is an ethylene-releasing chemical, will promote fruit ripening and can advance maturity, accelerating fruit abscission and softening thus negatively impacting fruit storability. ReTain® (active ingredient: Aminoethoxyvinylglycine (AVG), Valent USA) will inhibit ethylene production, delaying fruit ripening, while Harvista® (active ingredient: 1-Methylcyclopropene (1-MCP), AgroFresh), will bind to ethylene receptors in the fruit, blocking its perception, preventing fruit response to ethylene and therefore delaying ripening. ReTain® and HarvistaTM will allow keeping fruit on the tree for a longer time, preventing fruit drop and maintaining a firmer texture that can contribute to a longer storability.
This article appears on August 19, 2021, Volume 12, Issue 5 of the Vegetable and Fruit News