Fruit juices sources

Pectin is used in foods in two forms, high methoxyl pectin and low methoxyl pectin. High methoxyl pectin is the form normally found in fruit while low methoxyl pectin is a chemically modified pectin. Pectins are acidic polysaccharides that occur in the cell walls of fruit. The commercial source of pectin is either citrus peel or apple pomace. The citrus peel is the residue from the production of citrus juices while apple pomace is the residue of cider production. Thus pectin is a by-product of either cider or fruit juice production. 

Forsyth and coworkers63 found organotin compounds in fruit juices. Thus juices from apple and passion fruit contained low or undetectable levels of butyl-, phenyl- and octyltin compounds. Octyltins were present in juices sold in containers constructed of poly(vinyl chloride) but not in those made from poly(ethyleneterephthalate). Therefore, the likely source of the octyltin was the PVC container material63. 

Natural products such as wine, fruit juices, flavors, oils, and honey are prime targets for fraudulent adulteration because of their high prices. Sophisticated analytical methods (perhaps including isotope abundance measurements) are required to detect whether natural ingredients have been mixed with ones from cheaper synthetic sources. Isotope abundance is markedly different for natural vs. synthetic molecules and these differences can be exploited to detect adulteration. Several examples follow. 

A normal diet contains a sufficient amount of both sodium and potassium. The body has specific mechanisms for regulating the Na ion concentration, which is important in the control of blood pressure (Chapter 22). However, there is less potassium in the normal diet and it may not always be sufficient (e.g. if the sweating rate is high). Fruit and fruit juices are good natural sources of this electrolyte. 

Hydrolysis of mannan-type polysaccharides by P-mannanase is dependent on substitution on and within the main-chain as well as the source of the P-mannanase employed. Characterisation of reaction products can be used to define the sub-site binding requirements of the enzymes as well as the fine-structures of the polysaccharides. Action of c/xt/o-arabinanase and em/o-galactanase on arabinans and arabinogalactans is described. Specific assays for ndo-arabinanase and arabinan (in fruit-juice concentrates) are reported. 

Fruit juice contains both catechins and flavonols. Apple juice is one of the richest juice sources of catechins (containing 6.3 mg (—)-epicatechin/100 ml and 0.8 mg (+)-catechin/ 100 ml) whereas cranberry juice contains the most flavonols, mainly in the form of quercetin and myricetin (17.5 mg/100 ml and 4.7 mg/100 ml, respectively). 

A comprehensive and critical review of food flavonoid literature has led to the development of a food composition database for flavonols, flavones, procyanidins, catechins, and flava-nones. This database can now be used and continuously updated to estimate flavonoid intake of populations, to identify dietary sources of flavonoids, and to assess associations between flavonoid intake and disease. However, there is a need for better food composition data for flavones, procyanidins, and flavanones as current literature is sparse particularly for citrus fruits, fruit juices, and herbs. In addition, anthocyanin food composition data are lacking although validated methods of determination are becoming available. 

While potato tuber is an important source of starch, it also contains 30-35 g buffer-extractable protein per kg dry weight (Pots et al., 1999). Protein yield per hectare of potatoes has been estimated as 500-1000 kg. The aqueous solution remaining after industrial potato starch manufacture, i.e., the potato fruit juice, contains approximately 1.5% (w/v) of soluble protein, mainly... 

Citrus fruits and associated products (fruit juices, peeled fresh fruit) are a major dietary source of flavanones (Table 13) [35]. However, the distribution is quite scattered, and much higher concentrations are found in the solid tissues compared to the juice. For example, an individual drinking orange juice (250 ml) will have a daily flavone intake (as aglycones) in the range of 25-60 mg eating the flesh of a whole orange (200 g) will provide about 125-375 mg. 

The protocols presented here allow one to analyze the anthocyanins in fruit juices, natural colorants, and extracts from various anthocyanin sources. These profiles are useful for the identification of species, varieties, and for quality assessment of commercial products. They are also used to detect misbranding or adulteration of fruit products with other anthocyanin containing fruits, juices, or colorants. 

Apply a drop of a fruit juice or paste sample to a Brix refractometer, hold the refractometer perpendicular to a light source, and determine the initial Brix (percent soluble solids) value for the sample. 

The overwhelming majority of foods contain amino acids, either in the free form (e.g., fruit juice) or in the form of protein (partially hydrolyzed or intact). Proteins are polymers, and their monomeric units are amino acids. Predominantly, proteins are comprised of 20 amino acids (see Fig. 1). In addition, some structural proteins contain large amounts of hydroxyproline (e.g., collagen). Far less abundant is the amino acid hydroxy lysine. The principal sources of dietary amino acids for humans are proteins, which are enzymatically digested to liberate their constituent amino acids. 

Phenolic compounds are of interest due to their potential contribution to the taste (astrin-gency, bitterness, and sourness) and formation of off-flavor in foods, including tea, coffee, and various fruit juices, during storage. Their influence on the appearance of food products, such as haze formation and discoloration associated with browning in apple and grape products, is also significant. Furthermore, analysis of these phenolic compounds can permit taxonomic classification of the source of foods. The importance of each phenolic compound and its association with the quality of various foods is described further in Sec. IV, on food applications. 

The declaration of the quantity of key ingredients (fruit or fruit juice in soft drinks) has become law through quantitative ingredient declaration regulations in Europe, and where artificial sweeteners and carbohydrates are used together, an appropriate statement is necessary. A warning about the product being a source of phenylalanine must be incorporated when aspartame is used as a sweetener. 

Fruit juice is important in human nutrition far beyond its use as a refreshing source of liquid. Many fruits contain a variety of minor ingredients, particulary vitamins and minerals, as well as carbohydrates, which are the predominant solid component. Although fruit contains small amounts of protein and fat, these are not important ingredients of juices. 

Apart from the more obvious benefits of fruit juice, such as being a source of potassium, it contains other substances that have or are claimed to have useful pharmacological activity. For example, limonin and other related limonoid substances present in citrus fruit are believed to have a role in inhibiting certain forms of cancer. Sorbitol, which occurs in many fruit juices, has a laxative effect. 

Fructose syrup. In addition to the glucose/fructose syrups mentioned above, a fructose syrup has been produced using inulin as a source. Inulin is the fructose analogue of starch, and the chicory root is the standard source for commercial hydrolysis. Fructose syrups are usually too expensive for routine use in beverage production but they have been employed where a particular claim is to be made for fructose. They have also been used for the adulteration of fruit juices as they are chemically difficult to detect. Detection is possible at the sub-molecular level by techniques such as stable isotope ratio measurement. Fructose is also manufactured using sucrose as a starting material. 

Sedentary adults in a temperate climate need to consume about 21 of water per day, a figure that can substantially increase when high temperature and/or physical activity causes significant sweating. Soft drinks and fruit juices provide a valuable water source, as shown in Table 13.1. 

The only sources of NSP in soft drinks are fruit materials, gums and stabilisers such as sodium carboxymethylcellulose (CMC) and pectins. Of these items, only fruit juices are used in significant quantities. The NSP content of most fruits falls within the range 0.9-3.6% w/w but, as Table 13.4 shows, very little remains in processed juices. Citrus comminutes are conventionally considered to have the same NSP content as the corresponding fruit but if they are known to contain substantial amounts of peel extracts this should be accounted for in calculations. 

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