Introduction
- Juices are a product for direct consumption and are obtained by the extraction of cellular juice from fruits; this operation can be done by pressing or diffusion. It is a beverage made from the extraction or pressing of a natural liquid containing fruits or vegetables.
- Classifications include ‘‘natural juice’’ products obtained from one fruit, and ‘‘mixed juice’’ products obtained from the mixing of two or three juices of different fruit species or by adding sugar. Juices obtained by removal of a major part of their water content by vacuum evaporation or fractional freezing are defined as ‘‘concentrated juices.’’
- The extracted liquid is composed of water, soluble solids (sugars and organic acids), aroma and flavor compounds, vitamins and minerals, pectic substances, pigments, and, to a very small degree, proteins and fats. The various sugars, such as fructose, glucose, and sucrose, combined with a large number of organic acids (most important being citric, malic, and tartaric), help give the fruit its characteristic sweetness and tartness.
- During the ripening of fruits, a general decrease in acidity and starch as well as an increase in sugars is seen. Moreover, the formation of odors, breakdown of chlorophyll, and hydrolysis of pectic substances also occur. It must be noted that plant tissues continue to ripen after harvest. Finally, senescence occurs, at a rate accelerated by the increase in ethylene.