277 Improvement of Texture by Modifying Processing Conditions Lilia Ahrné*, Gerardo Gonzalez-Martinez, Ingegerd Sjöholm, Katarina Nilsson * SIK, The Swedish Institute for Food and Biotechnology, Department of Food and Biotechnology Box 5401, 402 29 Gothenburg, Sweden E-mail: lilia.ahrne@sik.se Keywords: potatoes, blanching, freezing, pectinmethylesterase, starch, microscopy Abstract Fruit and vegetable processors, faced with the challenge of gaining and maintaining a healthy position in the competitive fruit and vegetable sector, are optimising traditional processes towards product quality. Using frozen potatoes as a case study, the aim of this study was to evaluate the potential of improving the texture of potatoes by modifying the processing conditions. The texture of processed frozen potatoes is the result of the integral effect of the unit operations applied through the production chain. Production of frozen potatoes includes a blanching, a freezing, thawing/cooking step before being served. In this study, blanching temperatures from 70 to 97 °C up to 10 minutes were tested and combined with freezing by two freezing methods, impingement and air-blast freezing. The texture was measured after cooking of frozen potatoes in boiling water. Besides texture, water holding capacity, microstructural evaluation and pectinmethylesterase (PME) activity were determined. Blanching of potatoes prior to freezing can both improve water holding capacity and texture of potatoes, but this effect depends on the freezing rate and blanching temperature. Potatoes frozen with fastest freezing method are firmer and hold more water than the ones frozen by air-blast freezing. Blanching at 70 °C can lead to potatoes that after cooking retain a firmer texture, compared with blanching at 90 °C. The duration of the blanching treatment has also an important effect on texture changes. The studies of PME activity showed a good correlation between texture and PME for blanching at 90 °C, but for blanching at 70°C and longer times, the development of texture does not seem to be solely related to PME activity. Microstructural studies showed that the differences in texture are due to differences in the degree of starch gelatinisation and integrity of the cellular structure. INTRODUCTION Fruit and vegetable processors, faced with the challenge of gaining and maintaining a healthy position in the competitive fruit and vegetable sector, are optimising traditional processes towards product quality. Texture is one of the most important sensory characteristics of fruits and vegetables and one of the most affected by processing. Softening and subsequent loss of integrity of fruit and vegetable pieces during processing are common problems. Consumers want products with a firm, well-shaped and uniform texture all year around. However, the texture of fruits and vegetables received as raw materials by the food industry is not uniform. Factors like variety, maturity, and storage conditions, as well as growing and weather conditions influence the texture of fruit and vegetables. Therefore, there is a need to modify the processing conditions depending on the quality of the raw materials. Nevertheless there is very limited information about how to modify the process in order to produce a given texture. The texture/structure of processed fruits and vegetable products is the result of the integral effect of the unit operations applied through the production chain of such products. The thermal processes involved in the production and preparation of frozen vegetables such as blanching, freezing and subsequent home preparation (thawing and cooking) can greatly affect the texture of the product reaching the consumer’s table. A number of methods are available to the industry to avoid the excessive softening Proc. Int. Conf. Quality in Chains Eds. Tijskens & Vollebregt Acta Hort. 604, ISHS 2003