Firmer fruit

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Related tags: Cell wall, Dsm

Processors seeking an alternative approach to mechanical and heat
treatment of fruit pieces could benefit from the latest research
findings from the Dutch-based DSM group.

Processors seeking an alternative approach to mechanical and heat treatment of fruit pieces could benefit from the latest research findings from the Dutch-based DSM group.

Fruit treated with DSM's​ FirmFruit can, the company claims, 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.

DSM Food Specialties' proprietary enzymatic treatment can be applied to improve the texture, colour, shape aspect and mouthfeel of processed fruit and vegetables, without affecting the ingredients label. As its name implies, DSM's FirmFruit can improve fruit firmness, benefiting manufacturers who want to use 'firmer' fruit pieces in applications as wide ranging as processed tomato products, fruit preparations and yoghurts.

DSM's research has focused primarily on the challenges presented by processed tomatoes, although trials have been carried out to test the efficacy of FirmFruit in strawberries. 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. Since tomato pieces are particularly prone to damage during processing and cooking, especially when heated, any improvement to their shape, texture and firmness would be welcomed by manufacturers and processors.

The overall structure of a tomato makes it susceptible to damage during the various stages of processing. Softening and deterioration 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. Thus, the first stage of tomato processing must consist of thermal stabilisation to deactivate any endogenous enzyme activity. Thermal treatments employed to denature the endogenous enzyme activity do, however, have an adverse effect on the consistency and end product quality of the tomato.

To counterbalance these 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, thus contributing to the strength of the cell wall and increasing 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.

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 thus practically no reaction with calcium ions.

During recent industrial trials conducted by DSM, the technique was applied to tomato pieces and tomato sauce. In the tomato piece trial, a typical tomato processing sequence was followed - washing, screening, peel removal, cutting, second screening followed by mixing with sauce. Rapidase FP and additional calcium source being incorporated into the process at the juice addition point. Control and treated samples were measured for piece size/weight and firmness.

The results of the tomato piece trial were impressive. Even at dilute levels (1000 ppm of Rapidase), the piece yielded (per cent weight) of tomato pieces was improved by 12 per cent and firmness by 13 per cent. The most dramatic improvements were achieved by combining the effects of Rapidase at 2000ppm with 1000ppm of calcium - generating over 26 per cent weight/weight improvement and over 100 per cent firmness improvement compared to control.

Greater piece identity in a reduced water content reduces minimal seasoning requirement - while FirmFruit treated products also benefited from better colour and appearance and enhanced mouthfeel.

In a second set of trials, similar tests were carried out to establish the benefits to be gained from adding Rapidase FP Super and additional calcium to tomato sauce. Similar synergistic effects between this technique and calcium were seen in the tomato sauce trials. Although calcium fortification achieved a viscosity improvement of 18 per cent, DSM's results showed that viscosity improvements of up to 32 per cent, without synerisis, could be made when both were added together.

DSM is continuing its research into the benefits of FirmFruit for tomato processors, and both batch and continuous process formulation recommendations have been developed. For example, initial studies have shown that when Rapidase FP Super is added with calcium source to whole, peeled tomatoes, cubes and sauces at 35-40 degrees celsius for 10 to 20 minutes before the products are canned, it is hoped that the manufacturers will be able to offer consumers tomato products that are firmer and more succulent.

The benefits of adding the PME enzyme to fruit processing is not limited to tomatoes, and further trials by DSM demonstrate its effectiveness on strawberries.The addition of Rapidase FP Super demonstrates a 50 per cent reduction in soluble pectin and a 57 per cent increase in firmness. FirmFruit also offers dairy manufacturers significant marketing advantages, for example, in yoghurt and other applications, where distinct strawberry pieces are perceived by consumers as only found in premium products.

DSM claims that the advantages for manufacturers and end-users alike are evident. FirmFruit can be easily incorporated into existing production processes and is a cost-effective alternative to traditional methods.

Related topics: Processing & Packaging

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