chapter  16
28 Pages

- Thermal Processing of Fruits and Fruit Juices

The proportion of fruits that are eaten after processing has greatly increased in the last decade, with in particular a remarkable expansion and diversiƒcation of fruit juices. Canning comes a far second, while fresh-cut (outside the scope of this chapter) and puréed products have also received renewed interest. There is a steady industrial demand for cooked chilled or frozen intermediate products, most of which are further processed, for example, in jams or frozen desserts. Concentrated juices are a commodity on the world market. As most fruits are of relatively low pH (lower than 4.5), the microbial safety of fruit products only requires mild heat treatments (pasteurization) even for long-term stability at room temperature. The limiting factors in thermal treatments of fruits are therefore more linked to physicochemical properties. The ƒrst limiting factor often is inactivation of endogenous enzymes, some of which can be relatively heat resistant. The typical example is pectin methylesterase, which is linked to cloud instability in fruit juices. The thermal treatments applied

16.1 Introduction .......................................................................................................................... 413 16.2 Microbial Considerations in Fruits Thermal Processing ...................................................... 414 16.3 Quality Assessments Considerations .................................................................................... 417 16.4 Applications of Thermal Processing .................................................................................... 417

16.4.1 Blanching .................................................................................................................. 418 16.4.2 Pasteurization ........................................................................................................... 418 16.4.3 Canned Food Products.............................................................................................. 419 16.4.4 Continuous Sterilization and Aseptic Processing ..................................................... 420

16.5 Quality Attribute Modiƒcations during Thermal Processing of Fruits ................................ 420 16.5.1 Texture ...................................................................................................................... 420

16.5.1.1 Thermal Softening of Fruits ...................................................................... 422 16.5.1.2 Rheological Behavior of Purees and Compotes ........................................ 423 16.5.1.3 Juice Cloud Stability .................................................................................. 423

16.5.2 Color and Image Analysis ........................................................................................424 16.5.3 Aroma Modiƒcation ................................................................................................. 426 16.5.4 Nutritional Impact of Fruit Heat Processing ............................................................ 426

16.5.4.1 Vitamin C ................................................................................................... 426 16.5.4.2 Carotenoids ................................................................................................ 428 16.5.4.3 Dietary Fiber .............................................................................................. 429

16.6 Conclusions ........................................................................................................................... 429 Nomenclature ................................................................................................................................. 429 References ...................................................................................................................................... 430

to jams are also conditioned by the physical properties of the ƒnal products and the need to reach high sugar concentrations while ensuring pectin homogeneous distribution throughout the product. In fruit juice concentrates or to a lesser extent puréed products, cumulative thermal treatments will be dominated by the evaporation steps.