P1: SFK/UKS BLBS102-c28 P2: SFK BLBS102-Simpson March 21, 2012 13:54 Trim: 276mm X 219mm Printer Name: Yet to Come 28 Biochemistry of Fruit Processing Raw apple Washing and sorting Disintegrator Juice extraction Enzyme treatment Filtration Evaporation Standardization Storage Figure 28.4 Apple juice and concentrate flow chart other methods) Juice yield from different types of extraction varies from 75% to 95%, and depends on many factors including the cultivar and maturity of the fruit, the type of extraction, the equipment and press aids, the time, temperature, and the addition and concentration of the enzyme to the apple mash (Fig 28.4) Enzyme Applications Enzyme applications in the apple juice processing follow the extraction, especially when producing a clarified type of juice The main objective is to remove the suspended particles from the juice (Smock and Neubert 1950) The soluble pectin in the juice has colloidal properties and inhibits the separation of the undissolved cloud particles from the clear juice Pectinase hydrolyzes the pectin molecule so it can no longer hold juice The treatment dosage of pectinase depends on the enzyme strength and varies from one manufacturer to another A typical ‘3X’ enzyme dosage is about 100 mL per 4000 liters of raw juice Depectinization is important for the viscosity reduction and the formation of galacturonic acid groups that helps flocculate the 563 suspended matter This material, if not removed, binds to the filters, reduces the production, and can result in a haze formation in the final product There are two methods of enzyme treatment commonly used in the juice industry including (1) hot treatment where the enzymes are added to 54◦ C juice, mixed, and held for 1–2 hours; and (2) cold treatment where the enzymes are added to the juice at reduced temperature (20◦ C) and held for 6–8 hours The complete breakdown of the pectin is monitored by means of an acidified alcohol test Five milliliters of juice are added to 15 mL of HCl-acidified, ethyl alcohol Pectin is present if a gel develops in 3–5 minutes after mixing the juice with the ethanol solution The absence of gel formation means the juice depectination is complete In the cloud of the postprocessed juice, other polymers such as starch, and arabinans can be present and therefore, the clear juice is treated with alphaamylase and hemicellulase enzymes, in order to partially or completely degrade them Gelatin can be used to remove fragmented pectin chains and tannins from the juice Best results are obtained when hydrating 1% gelatin in warm 60◦ C water Gelatin can be added in combination with the enzyme treatment, bentonite, or by adding midway through the enzyme treatment period The positively charged gelatin facilitates the removal of the negatively charged suspended colloidal material from the juice Bentonite can be added in the range of 1.25–2.5 kg of rehydrated bentonite per 4000 L of juice Bentonite is also added to increase the efficiency of settling, protein removal, and prevention of cloudiness caused by metal ions For cloudy and natural apple juice, enzymes are usually not used The enzyme-treated, refined, and settled apple juice is then pumped from the settled material (lees) and further clarified by filtration The filtration of apple juice is done with or without a filter aid The major types of filters are pressure leaf, rotary vacuum, frame, belt, and Millipore filters To obtain the desired product color and clarity, most juice manufacturers use a filter medium or filter aid in the filtration process The filter media include diatomaceous earth, paper pulp pads, cloth pads or socks, and ceramic membranes to name a few The filter aid helps to prevent the blinding of the filters and increase throughput As the fruit matures, more filter aid will be required Several types of filter aids are available, in which the most commonly used is diatomaceous earth or cellulose-type materials Additional juice can be recovered from the tank bottoms or “lees” by centrifugation or filtration This recovered juice can be added to the raw juice before filtration Diatomaceous earth, or kieselguhr, is a form of hydrated silica It has also been called fossil silica or infusorial earth Diatomaceous earth is made up of the skeletal remains of prehistoric diatoms that were single-cell plant life and is related to the algae that grow in the lakes and oceans Diatomaceous earth filtration is a three-step operation: (1) first, a firm thin protective precoat layer of filter aid, usually of cellulose, is built up on the filter septum (which is usually a fine wire screen, synthetic cloth, or felt); (2) the use of the correct amount of a diatomite body feed or admix (about 4.54 kg per 3000 cm2 of filter screen); and (3) the separation of the spent filter cake from the septum prior to the next filter cycle Prior to the filtration, centrifugation may be used to remove high-molecular weight suspended solids P2: SFK BLBS102-Simpson March 21, 2012 13:54 Trim: 276mm X 219mm 564 Printer Name: Yet to Come Ions and molecules Part 5: Fruits, Vegetables, and Cereals 0.1 nm R O nm Colloids U F 0.3 µ Microparticles P1: SFK/UKS BLBS102-c28 M F F 10 µ µ = 1000 nm Figure 28.5 Membrane filtration RO, reverse osmosis; UF, ultrafiltration; MF, microfiltration; F, filtration In some juice plants, high-speed centrifugation is used prior to the filtration This centrifugation step reduces the solids by about 50%, thus minimizing the amount of filter aid required The filtration process is critical, not only from the point of view of production, but also for the quality of the end product Both pressure and vacuum filters have been used with success in juice production (Nelson and Tresler 1980) A recent development in the juice industry is the membrane ultrafiltration Ultrafiltration, based on membrane separation, has been used with good results to separate, clarify, and concentrate various food products Ultrafiltration of apple juice will not only clarify the products, but depending on the size of the membrane, will also remove the yeast and mold microorganisms common in apple juice (Fig 28.5) Apple Juice Preservation Preservation of apple juice can be achieved by refrigeration, pasteurization, concentration, chemical treatment, membrane filtration, or irradiation The most common method is pasteurization based on temperature and time of exposure The juice is heated to over 83◦ C, held for minutes, filled hot into the container (cans or bottles), and hermetically sealed The apple juice is held for minute at 83◦ C and then cooled to less than 37◦ C When containers are closed hot and then cooled, vacuum develops, reducing the available oxygen that also aids in the prevention of microbial growth After the heat treatment, the juice may also be stored in bulk containers Aseptic packaging is another common process where, after pasteurization, the juice is cooled and packed in a closed, commercially sterile system under aseptic conditions This process provides shelf-stable juice in laminated, soft-sided consumer cartons, bag-in-box cartons, or aseptic bags in 200–250 liter drums Apple juice concentration is another common method of preservation The single-strength apple juice is concentrated by evaporation, preferably to 70◦ or 71◦ Brix By an alternate method, the single-strength juice is preconcentrated by reverse osmosis to about 40◦ Brix, then further concentrated by evaporation methods The reduced water content and natural acidity make the final concentrated apple juice shelf stable at room temperature There are several evaporators used in apple juice production including rising film evaporators, falling film evaporators, and multiple effect tubular and plate evaporators Due to the heat sensitivity of the apple juice, the multiple-effect evaporator with aroma recovery is the most commonly used The general method in a multiple-effect evaporator is to heat the juice to about 90◦ C and capture the volatile (aroma) components by cooling and condensation This is followed by reheating the 20–25◦ Brix juice concentrate in the first stage to about 100◦ C and then concentrate it to about 40–45◦ Brix Another stage of heating and evaporation at about 50◦ C to 60◦ Brix, and final heating and concentration in the fourth stage to 71◦ Brix provides fully concentrated juice The warm concentrate is then chilled to 4–5◦ C prior to adjusting the Brix to 70◦ before barreling or bulk storage Chemicals such as benzoic acid, sorbic acid, and sulfite are sometimes used to reduce spoilage of unpasteurized apple juice, either in bulk or as an aid in helping to preserve refrigerated products Application of irradiation and ultrasonic sound are new emerging methods of preservation with high potential even though not fully accepted by consumers at this time Apple essence is recovered during the concentration of apple juice The identification of volatile apple constituents, commonly known as essence or aroma, has been the subject of considerable research In 1967, researchers at the USDA identified 56 separate compounds from apple essence These compounds were further refined by organoleptic identification, using a trained panel of sensory specialists These laboratory evaluations revealed 18 threshold compounds identified as “Delicious” apple compounds consisting of alcohols, aldehydes, and esters Three of the eighteen compounds had “apple-like aromas” according to the taste panel These were 1-hexanal, trans-2-hexenal, and ethyl, 2-methyl butyrate (Flath et al 1967, Somogyi et al 1996b) Processed Apple Products The popularity of blended traditional/tropical juice products has pushed the consumption of traditional fruit juices such as apple, orange, and grape juices to 25 liters in 2002, an increase of more than 24% from 1992 (Statistics Canada 2003) Apples are normally processed into a variety of products, although apple juice is the most popular processed apple product With a production of 465,418 metric tons of apple in 2001, Canada exported P1: SFK/UKS BLBS102-c28 P2: SFK BLBS102-Simpson March 21, 2012 13:54 Trim: 276mm X 219mm Printer Name: Yet to Come 565 28 Biochemistry of Fruit Processing 18,538 metric tons of concentrated apple juice For the same year, United States exported 25,170 metric tons of concentrated apple juice (FAO 2003) Apples for processing should be of high quality, proper maturity, of medium size, and uniform in shape Apples are processed into frozen, canned, dehydrated apple slices and dices, and different kinds of applesauce Apples that are unsuitable for peeling are diverted to juice processing Apple Sauce Diced or chopped apples with added sugar, preferably a sugar concentrate, are cooked at 93–98◦ C for 4–5 minutes in order to soften the fruit and inactivate polyphenol oxidase Sauce with a good texture, color, and consistency is produced with high quality raw apples and a good combination of time and temperature treatment Cooked applesauce is passed through a pulper of 1.65–3.2 mm finishing screen to remove unwanted debris and improve the texture Applesauce is then heated to 90◦ C and immediately filled in glass jars or metal cans The filled applesauce are seamed or capped at 88◦ C and cooled to 35–40◦ C after 1–2 minutes (Fig 28.6) There are various types of applesauce that include natural, no sugar added, “chunky”, cinnamon applesauce, and mixture of applesauce and other fruits such as apricot, peach, or cherry Raw apple Washing and sorting Peeling and coring Dicing/chopping A p p l e s a u c e First inspection Cooking Pulping/finishing Second inspection Vacuuming Preheating/filling Blanching/filing Seaming Seaming Holding/cooking Cooking Cooling Cooling Labeling/storage Labeling/storage Figure 28.6 A flow chart depicting steps in apple processing C a n n e d a p p l e s l i c e s P1: SFK/UKS BLBS102-c28 P2: SFK BLBS102-Simpson March 21, 2012 13:54 566 Trim: 276mm X 219mm Printer Name: Yet to Come Part 5: Fruits, Vegetables, and Cereals Sliced Apples Sliced apples have multiple uses and are preserved by many different methods such as canned, refrigerated, frozen, or dehydrated states About 85% of sliced apples are processed, whereas only 15% are refrigerated, frozen or dehydrated and frozen Apple slice texture is very important, as well as the consistency of the slice size, therefore, apples with firm flesh and high-quality, falling within a specified size range are desirable Apples are sliced into 12–16 slices and blanched after inspection for eventual defects The blanched apple slices are hot filled into cans and closed under steam vacuum after addition of hot water or sugar syrup The canned apples are heated at 82.2◦ C and immediately cooled to 37–40◦ C When bulk frozen, apple slices are vacuum treated and blanched and filled into 13–15 kg tins or poly-lined boxes The tins or boxes are then sealed, frozen, and stored at −17◦ C Individual quick frozen apple slices (IQF) are usually treated with sodium bisulfite after inspection Nitrogen (N2 ) and carbon dioxide (CO2 ) are the most popular freezing media From the vacuum tank, the apple slices pass through an IQF unit where the slices are individually frozen From the freezing unit, the slices are filled into tins or poly-lined boxes and stored frozen at −17◦ C or below Dehydrofrozen apple slices are dehydrated to less than 50% of their original weight and then frozen The dehydrofrozen slices are packed in cardboard containers or large metal cans with polyethylene liners and rapidly frozen before storing Frozen slices are thawed and then soaked in a combined solution of sugar, CaCl2 , and ascorbic acid, or bisulfite For fresh and refrigerated apple slices, the use of 0.1–0.2% calcium chloride, and ascorbate protects apple slices from browning and microbial spoilage Blanched slices resist browning for approximately days, but lose flavor, sugar, and acid This type of product has a very short shelf life Recently, the use of natural protein polymer coatings (NatureSeal) has shown promise in enhancing the shelf life and quality of fresh-cut apple products Dried Apple Products Most processing cultivars are used for drying, but the best quality dried apple slices are obtained from “Red Delicious” and “Golden Delicious” apples A desirable quality attribute of apples used for drying is a high sugar/water ratio Color preservation and reduction in undesirable enzyme activities are achieved by the use of bisulfite There are two types of dried apple products including evaporated and dehydrated apples Evaporated apples are cut into rings, pie pieces, or dices and then dried to less than 24% moisture by weight The dehydrated apples, on the other hand, are cut into dices, pie pieces, granules, and flakes prior to drying to 3–0.5% moisture content Up to 300 ppm of bisulfite is used to prevent color deterioration The maximum allowed SO2 in dried apples in Europe is 500 ppm, whereas in United States, the limit is 1000 ppm Quality Control Apples contain several organic acids and as such, only a limited number of microorganisms can grow in them The most common microbes are molds, yeasts, aciduric bacteria, and certain pathogens such as E coli O157:H7, capable of growing at low pH (Swanson 1989) Several approaches to quality management are available today including total quality management (TQM), statistical quality control (SQC), and hazard analysis critical control points (HACCP) Biochemical Composition and Nutritional Value of Processed Apples The nutritive value of most processed apple products is similar to the fresh raw product Apple products are sources of potassium, phosphorus, calcium, vitamin A, and ascorbic acid Glucose, sucrose, and fructose are the most abundant sugars Dried or dehydrated apples have a higher energy value per gram tissue due to the concentration of sugars (Tables 28.4 and 28.5) The nutritional value of apples, and fruits in general, is enhanced by the presence of flavonoids More than 4000 flavonoids have been identified to date There are many classes of flavonoids of which flavanones, flavones, flavonols, isoflavonoids, anthocyanins, and flavans are of interest Flavanones occur predominantly in citrus fruits, anthocyanins, catechins, and flavonols are widely distributed in fruits, and isoflavonoids are present in Table 28.5 Nutrients in Fruits and Processed Products (454 g) Apples Raw fresh Applesaucea Unsweetened Juice Apple juice Frozen sliceda Apple buttera Dried, 24% Dehydrated, 2% Food Energy (kcal) Protein (g) Fat (g) Carbohydrate (g) Calcium (mg) Phosphorus (mg) Iron (mg) 242 413 186 213 422 844 1247 1601 0.8 0.9 0.9 0.5 0.9 1.8 4.5 6.4 Source: Composition of foods Agriculture Handbook No a With sugar 2.5 0.5 0.9 0.1 0.5 3.6 7.3 9.1 60.5 108.0 49.0 54.0 110.2 212.3 325.7 417.8 29 18 18 27 23 64 141 181 42 23 23 41 27 163 236 299 1.3 2.3 2.3 2.7 2.3 3.2 7.3 9.1 P1: SFK/UKS BLBS102-c28 P2: SFK BLBS102-Simpson March 21, 2012 13:54 Trim: 276mm X 219mm Printer Name: Yet to Come 567 28 Biochemistry of Fruit Processing OH B OH Citrus O A C OH O Flavonone OH Anthocyanin OH O + Blueberries Cherries Wine OH OH OH OH O Catechin OH OH OH OH O OH OH Apples Peaches Tea OH OH OH Biflavan O OH OH Flavans OH OH Figure 28.7 Chemical structures of fruit flavonoids The propanoid structure consists of two fused rings “A” is aromatic ring and “C” is a heterocyclic ring attached by carbon–carbon bond to “B” ring The flavonoids differ in their structure at the “B” and “C” rings legumes Structurally, flavonoids are characterized by a C6 -C3 C6 carbon skeleton (Fig 28.7) They occur as aglycones (without sugar moieties) and as glycosides (with sugar moieties) Processing may decrease the content of flavonoids by up to 50%, due to leaching into water or removal of portions of the fruit such as the skin, that are rich in flavonoids and anthocyanins It is estimated that the dietary intake of flavonoids may vary from 23 mg/d to 1000 mg/d in various populations (Peterson and Dwyer 1998) Flavonoids are increasingly recognized as playing potentially important roles in health including but not limited to their roles as antioxidants Epidemiological studies suggest that flavonoids may reduce the risk of developing cardiovascular diseases and stroke Flavanones The major source of flavanones is citrus fruits and juices Flavanones contribute to the flavor of citrus, for example, naringin found in grapefruit provides the bitter taste, whereas hesperidin, found in oranges is tasteless Flavonols The best-known flavonols are quercetin and kaempferol Quercetin is ubiquitous in fruits and vegetables Kaempferol is most common among fruits and leafy vegetables In fruits, flavonols and their glycosides are found predominantly in the skin Myricetin is found most often in berries ... (mg) 242 413 186 213 422 84 4 1247 1601 0 .8 0.9 0.9 0.5 0.9 1 .8 4.5 6.4 Source: Composition of foods Agriculture Handbook No a With sugar 2.5 0.5 0.9 0.1 0.5 3.6 7.3 9.1 60.5 1 08. 0 49.0 54.0 110.2... or capped at 88 ◦ C and cooled to 35–40◦ C after 1–2 minutes (Fig 28. 6) There are various types of applesauce that include natural, no sugar added, “chunky”, cinnamon applesauce, and mixture of... and time of exposure The juice is heated to over 83 ◦ C, held for minutes, filled hot into the container (cans or bottles), and hermetically sealed The apple juice is held for minute at 83 ◦ C and