Managing Stone Fruit Firmness
Firmness of fruit flesh is affected by a wide range of parameters. Proper crop nutrition helps to achieve adequate firmness levels.
There are a number of variables that define stone fruit quality requirements. Quality standards differ depending on the stone fruit type, growth region and the market.
Crop fertilizer practices have a strong influence on external fruit quality such as coloration and the amount of cracking or splitting.
The degree and level of these external factors can make a big difference to crop price and marketability.
Acceptable size and grade varies according to market and most countries set their minimum standards. Splitting, cracking and other physiological disorders are undesirable.
Fruit firmness is particularly important to the bite quality of the fruit. Optimum firmness levels also contribute to a better resistance against physiological disorders (breakdown of fruit flesh, pitting) and fruit rots during storage.
Flavour and taste is related to the level of Total Soluble Solids (TSS), acidity and juiciness of the fruit. The TSS/acid ratio provides an indication of the taste of the fruit – sweet or bitter.
The Vitamin C or ascorbic acid content is perceived by consumers as being beneficial for a healthy nutrition.
Calcium has a major role to play in maximizing fruit quality by providing firm fruit, with minimal internal breakdown or rots and tougher skin. Calcium also increases TSS and sugar content, flavour, taste and juiciness.
Potassium has a major role to play in improving fruit quality by boosting the TSS content and colour of fruit. However, supplies need to be in balance as over-availability can lead to other quality problems due to competition between K, Ca and Mg uptake.
Increasing nitrogen supply can increase fruit acidity, improving vitamin C contents. However, overuse of N delays maturity, softens the flesh and thins the skin. It can also reduce fruit colour and TSS contents. This is due to the improved yield and larger fruit size, which dilutes the level of TSS in the fruit.
Phosphorus increases fruit colour by boosting anthocyanin content. It also helps minimize a range of storage disorders.
Iron is important in boosting growth and, as a result, maintaining fruit fill and sugar content.
Boron and copper help improve skin strength, minimizing cracking.
Firmness of fruit flesh is affected by a wide range of parameters. Proper crop nutrition helps to achieve adequate firmness levels.
Splitting or cracking, usually as a result of rainfall prior to harvest, is a serious problem in all stone fruit, especially in cherries and plums, as it renders fruit unmarketable.
Produce buyers constantly prefer redder fruit. Some varieties develop redder colour than others.
The main cause for internal breakdown is an inadequate physiological growth leading to a breakdown of internal tissues.
Pitting is a significant problem in cherries as a result of poor handling and storage conditions.
Storage rots are caused by a range of pathogens including Botrytis cinerea, Geotrichum, Alternaria, Phomopsis, Penicillium sp, Rhizopus, Saccharomyces sp, and Cladosporium sp.
The TSS or ‘sugar content’ measures and includes the carbohydrates, organic acids, proteins, fats and minerals of the fruit.