Minimal deterioration for fruit ingredients

Food ingredients company DSM claims this week that food manufacturers seeking an alternative approach to mechanical and heat treatment of fruit pieces could benefit from recent research carried out on tomatoes by the company.

DSM reports that fruit treated with its enzymatic treatment FirmFruit can be incorporated into a variety of products with minimal deterioration, demonstrating a marked increase in fruit identity, firmness and stability. Many fruits, including red berry fruits, apples, pears and tomatoes - whether fresh, frozen or thawed - can be processed, the company maintains.

The enzymatic treatment FirmFruit, can, according to DSM, be applied to improve the texture, colour, shape aspect and mouthfeel of processed fruit and vegetables, without affecting the ingredients label.

The latest research from DSM focused primarily on the challenges presented by processed tomatoes. As the quality and textural characteristics of diced, peeled and associated tomato products become increasingly important to the food industry, studies have been undertaken to improve the texture of tomatoes using thermal, enzymatic and mechanical methods.

Tomato pieces are particularly prone to damage during processing and cooking, especially when heated, and any improvement to their shape, texture and firmness might be beneficial to manufacturers and processors.

DSM​reports that softening and deterioration of tomatoes during ripening and post-harvest handling is due to the evolution of cell wall polysaccharides, primarily of pectic substances, in which several fruit endogenous hydrolases are involved. Endo-polygalacturonase activity is the main activity responsible for tomato softening as the pectin molecular weight decreases, and is even more active after fruit crushing.

Consequently, the company recommends that the first stage of tomato processing should consist of thermal stabilisation to deactivate any endogenous enzyme activity. Thermal treatments employed to denature the endogenous enzyme activity have an adverse affect on the consistency and end product quality of the tomato.

To counterbalance the above negative effects, it is common practice in the tomato industry to add calcium chloride to the product to increase its firmness. The calcium ions react with free carboxyl groups of tomato pectin to produce a polymeric network of calcium pectate, and contribute to the strength of the cell wall and increase the product firmness. Calcium addition alone, however, is not sufficient to provide the improved functionality sought by the industry.

The key structural element in creating and preserving firm fruit is pectin. The texture of fruit and vegetables is attributed to the structural integrity of the primary cell wall (consisting of cellulose micro-fibrils that are parallel aligned and cross linked with hemicellulosic xyloglucan polymers) and the middle lamella. In particular, pectin of the middle lamella acts as an adhesive between adjacent cells, providing structure and cohesion to the fruit tissue. DSM's FirmFruit concept involves the application of Rapidase FP Super to whole fruit, fruit pieces or fruit purée during processing into fruit preparation or fruit sauce. Rapidase FP Super is a pure fungal pectinmethylesterase (PME) enzyme - derived from a non-genetically modified Aspergillus niger​ strain - which generates a demethylation of in situ fruit pectin. The demethylated pectin then gelifies at acid pH and combined with the naturally occurring calcium present in fruit, forms a strong pectate network within the fruit, thereby increasing its consistency and viscosity.

DSM maintains that the success of the Firm Fruit concept is based on the ability of Rapidase" FP Super to alter fruit gelification characteristics from natural high methylated (HM) pectin to low methylated (LM) pectin. Since low methoxyl pectins have less than 50 per cent methoxylated polygalacturonic acid units, they provide better gelling properties - improving the firmness, size and identity of fruit pieces. High methoxyl pectins have more than 50 per cent methoxylated polygalacturonic acid units, and have practically no reaction with calcium ions.