Đề tài Production of fructose syrup from Jerusalem Artichoke

Table of Content

Table of figures

Table of tables

Chapter 1: Introduction . 1

I. Production of fructose syrup in the world: . 1

1. Manufacturing of high-fructose corn syrup (HFCS): . 2

1.1. Corn wet milling: . 2

1.2. Hydrolysis: . 4

1.3. Isomerization: . 5

1.4. Fractionation: . 5

2. Overview of the world situation: . 5

3. Factors affecting production: . 8

II. Materials in processing of fructose syrup from Jerusalem artichoke: . 8

1. Jerusalem Artichoke: . 8

1.1. Scientific classification of Jerusalem Artichoke: . 9

1.2. Compositional characteristics: . 18

2. Inulinase: . 29

3. Saccharomyces cerevisiae: . 29

Chapter 2: Processing technology of fructose syrup from Jerusalem

artichoke: Production-line schema . 32

Chapter 3: Processes in the fructose syrup production-line from

Jerusalem artichoke . 33

I. Preliminary treatment: . 33

1. Aim: . 33

2. Transformation of raw materials:. 33

2.1. Physical changes: . 33

2.2. Chemical changes: . 33

3. Affecting factors: . 33

4. Technical parameters: . 33

II. Cutting: . 34

1. Aim: . 34

2. Transformation of raw materials:. 34

3. Effective factors: . 34

III. Milling: . 34

1. Aim: . 34

2. Transformation of raw materials:. 34

3. Effective factors: . 34

4. Technical parameters: . 34

IV. Extraction: . 35

1. Aim: . 35

2. Transformation of raw materials:. 35

2.1. Physical changes: . 35

2.2. Chemical changes: . 36

2.3. Physical chemical changes: . 36

3. Effective factors: . 36

4. Technical parameters: . 36

V. Filtration: . 37

1. Aim: . 37

2. Transformation of raw materials:. 37

3. Effective factors: . 37

4. Technical parameters: . 37

VI. Ultrafiltration: . 38

1. Aim: . 38

2. Transformation of raw materials:. 38

2.1. Physical changes: . 38

2.2. Chemical changes: . 39

3. Effective factors: . 39

4. Technical parameters: . 39

4.1. First ultrafiltration step: . 40

4.2. Last ultrafiltration step: . 40

VII. Hydrolysis: . 40

Conventional method: . 40

1. Aim: . 40

2. Transformation of raw materials: . 40

3. Effective factors: . 41

4. Technical parameters:. 41

Inulinase enzyme method: . 42

1. Aim: . 42

2. Transformation of raw materials: . 42

3. Effective factors: . 42

4. Technical parameters:. 42

VIII. Propagation: . 46

1. Aim: . 46

2. Transformation of raw materials:. 46

3. Effective factors: . 46

4. Technical parameters: . 46

IX. Sterilization: . 47

1. Aim: . 47

2. Transformation of raw materials:. 47

2.1. Biologycal changes: . 47

2.2. Physical changes: . 47

2.3. Chemical changes: . 48

3. Effect factors: . 48

4. Technical parameters: . 48

X. Fermentation: . 49

2. Transformation of raw materials:. 49

2.1. Microbial changes: . 49

2.2. Chemical physical changes: . 49

3. Effective factors: . 50

4. Technical parameters: . 50

4.1. Fermentation using mutant Saccharomyces cerevisiea ATCC 36859: . 50

4.2. Fermentation using immobilized mutant Saccharomyces cerevisiea ATCC 36859: . 50

XI. Activated charcoal treatment: . 53

1. Aim: . 53

2. Transformation of raw materials:. 53

2.1. Physical changes: . 53

2.2. Chemical physical changes: . 53

2.3. Biological: . 53

3. Affecting factors: . 53

4. Technical parameters: . 53

XII. Concentration: . 54

1. Aim: . 54

2. Transformation of raw materials:. 54

2.1. Physical changes: . 54

2.2. Physical chemical changes: . 54

2.3. Microbiological changes: . 54

3. Affecting factors: . 54

4. Technical parameters: . 54

Chapter 4: Product . 56

I. Physical chemical characteristics of Product: . 56

II. Microbiological characteristics: . 57

III. Organoleptic characteristics: . 57

Chapter 5: High-fructose syrup application . 58

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rs after desiccation. The extracts from such pretreated tubers contained more than 50% of total solids and diffusion batteries from the beet sugar industry have been found suitable for diffusion of sugars from the desiccated tubers. Extraction juice from fresh tubers may be condensed in an evaporator and stored for long periods of time. Underkofler et al. successfully stored concentrated juice (containing more than 50% solids) under a CO2 atmosphere. Various other methods by which the Jerusalem artichoke may be stored have been reported in the literature. Artigas and Jan found that acidification of tuber pieces (1 cm 3 or less) with 26% (v/v) HCl (aq) resulted in their successful preservation over a period of 4 months. Extracted juice, after acidification to pH 1.5-2.0 with 2% HC1 (aq), was observed to remain unchanged for 6 months. Addition of maleic hydrazide has also been used to prolong storage time. Electromagnetic radiation in the X-ray range (10 -9 ÷ 10 -11 in wavelength) has been studied by Patzold and Kolb in the interest of increasing effective storage time. They found that irradiation of tubers with 250-16000 RÖntgens inhibited germination and decreased losses of water, carbohydrates and Vitamin C during prolonged storage. It is apparent that the choices of storage method will be greatly influenced by the characteristics of tuber end-use. As food or fodder for livestock, it would be sufficient to store the artichokes such that tuber damage and disease is minimized. Cold storage or over-wintering in the soil is PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 18 inexpensive and satisfactory for this purpose. If the crop is to be used as a carbohydrate source for fermentation processes, disease must be controlled as well as native hydrolase activity preserved. It is necessary to keep the total reducing sugar content high; however, the ratio of fructose to glucose is not of prime importance. The endogenous hydrolysis of long-chain fructosans may, in fact, be preferred. Cold storage in silos may again be the most efficient method in this case. For use in the production of high-fructose containing syrups, it will be necessary to keep the fructose/glucose ratio as high as possible. This may be accomplished by extracting and condensing the juice through evaporators, dehydration of the tubers, or storage under narcotic vapors. These methods are very effective yet much more expensive than simple freezing. It is well known that longer processing periods utilize the working capital of industry much more efficiently than shorter lengths of operation. For Jerusalem artichoke production to be economical on a full commercial level, large-scale storage studies must be conducted to ensure that a continuous feedstock supply of reliable quality is available to. the process. It is possible that combinations of two or more methods may be the most effective and economical in some cases. 1.2. Compositional characteristics: Results from the proximate analysis of various Jerusalem artichoke samples also depend highly on the cultivation characteristics, harvest dates, time of analysis, and variety of the plant. In general, the composition of the tubers and aerial parts may be summarized as shown in Table 6. Each component is discussed in more detail below. Table 6: Composition of Tubers and Tops of the Jerusalem Artichoke (fresh weight basis) PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 19 1.2.1. Carbohydrates:  Inulin and inulides: Inulin is a natural storage polymer found widely in plants. Inulin is a linear polymer of D- fructose joined by β( 2 - 1) linkages and terminated with a D-glucose molecule linked to fructose by an α(1 ~ 2) bond, as in sucrose (Modler, 1994). . Inulin is a polydisperse fructan that ranges in its degree of polymerization (DP) from 2 to 60, or higher. The terminology used to identify these carbohydrates is not consistent. Often, the name of inulin is used to describe all such polysaccharides in the artichoke. Stauffer et al. have reported inulin to be those carbohydrates of the form described above, with a degree of polymerization (dp) from 9-35. However, other researchers state that only those polyfructans of 30 or more moieties in length may be considered as inulin. Under this definition, the content of inulin in the artichoke may in fact be quite low, while shorter-length oligosaccharides are more prevalent. This distinction is important since the longer-chain polyfructans behave quite differently in solution (i.e. variation of solubility limits in water or aqueous ethanol) and also exhibit much higher fructose to glucose ratios than do the shorter-chain molecules (an important trait for maximal fructose recovery). FIG 9. Structure of inulin For our purposes, inulin will be defined as polyfructans with dp ~ 30 or more. The term “inulides” will be used to describe those polysaccharides of 3-30 monomers in length. PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 20 Inulin is named from the plant Inula helenium and is the most fully studied polysaccharide of the Compositae family. It was first isolated from the tubers of the Jerusalem artichoke by Rose in 1804. Natural sources of inulin:  Elecampane (Inula helenium)  Dandelion (Taraxacum officinale)  Wild Yam (Dioscorea spp.)  Jerusalem artichoke (Helianthus tuberosus)  Chicory (Cichorium intybus)  Jicama (Pachyrhizus erosus)  Burdock (Arctium lappa)  Onion (Allium cepa)  Garlic (Allium sativum)  Agave (Agave spp.)  Yacón (Smallanthus sonchifolius spp.)  Camas (Camassia spp.) In this seminar, we used Jerusalem Artichoke. The distinction between inulin and shorter-chain inulides has arisen mainly from their differential solubility in aqueous solutions. The inulides are readily soluble in cold water, whereas the inulin component will not quantitatively dissolve unless the water is heated. Spontaneous precipitation of inulin is achieved if the solution is then cooled appreciably to freezing. The addition of ethanol (about 50% v/v) to artichoke juice will flocculate inulin. This flocculation process is slow and lasts months after addition of ethanol. Thus, it is impossible to designate a specific fraction of carbohydrate as being soluble or insoluble in aqueous ethanol. As well as ethanol, Bacon and Edelman found that addition of 7-20 volumes of acetone would precipitate inulin along with impurities. Physico-chemical properties of artichoke inulin: The physico-chemical characteristics of artichoke inulin are compared with samples of standard and high performance chicory inulin in Table 7. Artichoke inulin is moderately soluble in water (maximum 5% at room temperature), it has a bland neutral taste, without any off-flavour or aftertaste, and is not sweet. Therefore, it combines easily with other ingredients without modifying delicate flavours. For reasons of growing interest in the food and pet food industries, the short chain inulins have to be separated from their long chain analogues, because their properties (digestibility, prebiotic activity and health promoting potential, caloric value, sweetening power, water binding capacity, etc.) differ substantially (van Loo and Hermans, 2000; van Leeuwen et al., 1997; De Gennaro et al., 2000). The method applied here for artichoke inulin preparation produced high molecular weigh fractions of the polymer, and made further fractionation procedures (Moerman et al., 2004) by precipitation from water/solvent mixtures necessary. The process is ideal for food applications. PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 21 Artichoke inulin showed a high DPn value (DPn = 46) when compared with inulins from different sources (DPn = 26, 24, and 43 for Jerusalem artichoke, chicory, and dahlia inulin, respectively). The high average degrees of polymerization of artichoke inulin make its properties closer to those of high performance chicory inulin and it could be used for similar applications in the food industry. For instance, when used for replace fat inulin, mixed with water or an aqueous solution, forms a particle gel network resulting in a creamy structure with a spreadable consistency, which can easily be incorporated into foods to replace up to 100% of the fat (Franck, 2002). Artichoke inulin could also be used in combination with gelling agents such as gelatin, alginate, k- and i-carrageenans, gellan gum and maltodextrins. It also improves the stability of foams and emulsions, such as aerated desserts, ice creams, table spreads and sauces. This inulin could, therefore, replace other stabilisers in different food products (Franck, 2002). The hydrolysate of this material showed a major content of fructose and a smaller one of glucose as determined by GC–MS experiments. A comparison of gas chromatograms for different inulins is shown in Fig. 1. Three major peaks with retention times at 10.1 ± 0.04, 10.3 ± 0.01 and 11.65 ± 0.03 min were characteristic for the hydrolysates of all the inulins studied. Mass spectra of these peaks correspond to fructose with authentic samples of this monosaccharide used as standard. The FT-IR spectrum for artichoke inulin was essentially identical to chicory inulin showing OH stretch (3353 cm -1 ) and carbonyl bands (1745 cm -1 ) characteristic of inulin (Wu and Lee, 2000). Table 7: Health Effect: Inulin is a plant-derived carbohydrate with the benefits of soluble dietary fiber. It is not digested or absorbed in the small intestine, but is fermented in the colon by beneficial bacteria. Functioning as a prebiotic, inulin has been associated with enhancing the gastrointestinal system and immune system. In addition, it has been shown to increase the absorption of calcium and magnesium, influence the formation of blood glucose, and reduce the levels of cholesterol and serum lipids (Coudray et al., 1997; Niness, 1999). Therefore, inulin obtained from several Compositae (Jerusalem artichoke, artichokes, chicory, dahlias, and dandelions) is a subject of PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 22 interest in many food research programs (Mitchell and Mitchell, 1995; Smits and Hermans, 1998; Silver and Brinks, 2000; Heyer et al., 1998; van Loo and Hermans, 2000). About 30–40% of people in Central Europe suffer from fructose malabsorption. Since inulin is a fructan, excess dietary intake may lead to minor side effects such as increased flatulence and loosened bowel motions in those with fructose malabsorption. It is recommended that fructan intake for people with fructose malabsorption be kept to less than 0.5 gram/serving. There are three types of dietary fiber; soluble, insoluble, and resistant starch. Insoluble fiber increases the movement of materials through the digestive system and increases stool bulk; it is especially helpful for those suffering from constipation or stool irregularity. Soluble fiber dissolves in water to form a gelatinous material. Some soluble fibres may help lower blood cholesterol and glucose levels. Inulin is considered a soluble fiber. It is used as a mostly indigestible soluble dietary fibre and thickener in foods. Inulin is less soluble than oligofructose and has a smooth creamy texture that provides a fat-like mouthfeel. Inulin and oligofructose are nondigestible by human intestinal enzymes, but they are totally fermented by colonic microflora. The short-chain fatty acids and lactate produced by fermentation contribute 1.5 kcal per gram of inulin or oligofructose. Inulin and oligofructose are used to replace fat or sugar and reduce the calories of foods like ice cream, dairy products, confections and baked goods.  Other carbohydrates: Little information is available on the concentration of various other carbohydrates in the tuber and tops of the Jerusalem artichoke. Stauffer et al. found that cellulose content of the tuber (as measured by acid detergent solubilization) ranged from 33-40% in carbohydrate-extracted pulp (dry basis) for four strains. Hemicellulose levels were found to be between 2.3 and 13%. The cellulose content in the aerial parts was found to be 20-40% of dry weight. The hemicellulose content of the tops has been observed to decrease as the plant develops, evidence of pectin and starch in the tubers and tops of the artichoke have been mentioned in the literature; however, quantitative data was not available.  Dynamic of accumulation of sugars in tops and tubers: Table 8 shows the changes in water-soluble carbohydrate accumulation and the distribution between tops and tubers of nine late-maturing cultivars. The sugars were stored in the stalks until the end of September and then, during October, were rapidly transferred to the tubers. The total ugar content of the plants chieved a maximumvalue in September during flowering and thenremained constant up to the middle of November. Only when the rainfall in September was sufficient to promote increased photosynthesis, as in 1984, was there a further increase of sugar in the tubers. In an early-maturing cultivar (D-19 of INRA collection) the sugar accumulation and distribution were similar, but occurred a month earlier. PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 23 Table 8: Changes in accumulation of water-soluble carbohydrates in tops and tubers of Jerusalem Artiochoke. Average of nine-maturing varieties.  Location and development of polyfructans: It has been found that inulin and inulides are present in all parts of the artichoke plant, with the possible exceptions of the upper parts of stems, petioles, and leaves. Bachmanowa, findings show also that carbohydrate distribution in the tuber is non-uniform, with a higher concentration in the central core (~16-18%) and concentration decreasing as the radial distance from the centre increases (to about 8-10% w/w, wet basis). Though the mechanisms and factors which control fructose metabolism in the Jerusalem artichoke are still not completely understood, a fairly complete model has been put forth by Edelman and Jefford. The model is summarized in Figs 10 and 11. These researchers give special significance to the trisaccharide, lV-fructosylsucrose (FS) as a key intermediate in the production of long-chain inulides. This intermediate is formed by the transfer of a fructose moiety from one sucrose molecule to another, which liberates glucose (see Step 1, Fig. 10). The step is catalyzed by sucrose-sucrose 1 F -fructosyltransferase (SST). The terminal fructosyl residue on the trisaccharide is transferred to a sucrose molecule within the storage vacuole by β(2→1)Fructan: (2→1)fructan 1-fructosyltransferase (FFT) located on the tonoplast (Step 2). Repeated transfer of a fructose monomer to the growing polyfructan occurs (Step 3) until chain termination takes place. This sequential transfer can lead to inulin (dp~35) since precipitated sphero-crystals of this material have been optically visualized within the vacuole. Both SST and FFT are specific for their substrates and contain no hydrolytic activity. Thus, hydrolytic inulases β(2 ~ 1)Fructan 1-fructanohydrolases are also present, which catalyze the depolymerization of the polyfructans. Two such enzymes with similar properties have been described (hydrolases A and B), which are distinguished by their relative activities on inulin and the inulides. These enzymes break only the β(2 ~ 1) linkage between a terminal fructosyl group and its adjacent fructose residue (see Fig. 11, Step 1). Fructose is then transported into the cell cytoplasm at the expense of energy (Step 2). The FFT enzyme at this point is free to transfer fructosyl groups among the chain ends of the oligosaccharides within the vacuole, while hydrolases continue to liberate fructose. Therefore, the final result is a rapid decrease of the average chain length of the polymers. PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 24 It is found that fluctuations in chain length occur with no net loss of carbohydrate from the tuber. With this in mind, and the fact that all inulides and inulin are terminated by a sole glucose residue, it is apparent that some mechanism must allow for the interconversion of glucosyl and fructosyl residues since their ratios must change. The Edelman and Jefford model can account for this by hexosephosphate isomerase activity in the traditional pathways of sucrose synthesis (Step 4 in Fig. 10 ; Step 3 in Fig. 11). At the onset of tuber initiation in late summer, there is a great shift of sucrose translocation toward the subterranean parts of the plant. The tubers rapidly enlarge, with a concomitant increase in polyfructans. FIG 10. PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 25 The SST enzyme appears to be the controlling factor of this process. This is supported by the findings that SST activity disappears rapidly from the tubers when growth has ceased. In addition, SST activity quickly falls off within a few days when growing tubers are freshly harvested. Invertase activity has also been shown to increase substantially during tuberization; however, Edelman and Jefford dispute its role in fructan metabolism. The hydrolytic enzymes also increase in activity during tuber maturation yet remain at high levels during dormancy. When tubers are freshly harvested and stored at low temperatures (~ 2°C), the hydrolase activity of the tissues seems to be accelerated. Field studies which have followed the transitory levels of various carbohydrates during Jerusalem artichoke development can be easily explained in terms of these enzymatic effects. In studies on the time dependent concentration of inulides of varying length during plant maturation it was found that separate polyfructans with dp > 7 could not be quantified due to insufficient resolution given by the gas-liquid chromatographic system used for analysis. However, it could be seen that monosaccharides and oligomers of dp 1-5, though initially present in large amounts, steadily decreased during plant maturation and tuber filling. Concurrently, longer-chain inulides and inulin increased in concentration. This process is reversed at approximately the 16th week FIG 11. PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 26 after sprouting (i.e. tuber maturation), at which point high-molecular weight carbohydrates are broken down to short-chain oligomers. These results closely follow the anticipated flux in fructosyltransferase and hydrolase activity. As a consequence of general chain length reduction occurring with little change in total carbohydrate levels, it would be expected that fructose/glucose (F/G) ratios should decrease upon termination of tuber filling. This result has been observed by a number of workers is shown in Table 9. Fleming and GrootWassink have reported constant F/G ratios in their study on the development of the Jerusalem artichoke. However, this observation is considered as anomalous and is attributed to specific agronomic conditions such as rainfall. It has been found that relative fructose concentrations rarely fall below 70% during normal fall harvest periods. A typical comparison of the relative abundance of monosaccharides, inulides, and inulin is shown in Table 10 for two strains of tubers grown in three successive seasons. The level of monosaccharides is generally low, although this may vary in relation to enzyme activity. Since the polymerization mechanism releases, free glucose whereas the hydrolytic steps liberate fructose, the relative concentrations of these monosaccharides are highly dependent upon the age at harvest and storage time of the sample. The levels of oligosaccharides and inulin are also closely related to these parameters for reasons discussed earlier. It is important to note the extreme variations in carbohydrate make-up witnessed across the two artichoke strains and, within the same strain, across the three seasons. It is apparent that the variety of the plant and prevailing seasonal conditions in the year it is grown elicit a great effect on Jerusalem artichoke composition. It has been reported that glucose and fructose are generated in the leaves of the Table 9: PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 27 artichoke plant and polymerization first occurs in the stem as the carbohydrate is translocated toward the developing tubers, thus, the interest has been placed on the artichoke stalks as possible sources of carbohydrate in addition to (or in place of) the tubers. 1.2.2. Protein content: Total nitrogen and protein levels in the Jerusalem artichoke remain relatively constant during plant growth. Table 11 compares the concentration of protein and various amino acids contained in the tubers and tops with that of potato tubers and forage beet roots. It was found that aerial parts of the artichoke contain a greater proportion of protein than do the tubers; however, crude protein levels in the tops may decrease if harvesting is substantially delayed. The Jerusalem artichoke contains a similar amount and distribution of amino acids as the fodder beet but amino acid levels in the potato tuber are almost consistently greater. The quality of this protein for human and livestock consumption will be discussed in the second part of this review. Table 11: 1.2.3. Minerals: The tubers of the Jerusalem artichoke contain a considerable amount of minerals. According to Conti and Eihe, ash content in the tuber is 1.2-4.7% and 4.7% of dry weight respectively. This value is equivalent to the ash content found in potato tubers. Reports by Rashchenko, that mineral content of the tuber increases to 32% of dry weight during plant growth probably reflects the consumption of storage carbohydrates in the tuber rather than any increases in ash levels. Table 10: PRODUCTION OF FRUCTOSE SYRUP FROM JERUSALEM ARTICHOKE SUPERVISOR: VAN VIET MAN LE 28 Vegetative biomass of this plant is found to contain two to three times the amount of ash than the tubers. Leaves are especially abundant in ash, where 12-16% of the total dry matter is of this material. A comparison between the mineral composition of the Jerusalem artichoke and the potato is given in Table 12. The level of each component in both plants is similar in most cases with the exceptions of Na, Fe, and Si oxides, The increased levels of Fe2O3 (triple that found in the potato) give the artichoke significance for the prevention of anaemia in livestock. 1.2.4. Vitamins: The levels of Vitamin C and H-carotene (precursor to Vitamin A) are found at their maximum during July and August for both the tubers and tops. Leaves exhibit the highest concentrations in July, with 371 mg/kg (d.m.) and 1662 mg/kg (d.m.) for carotene and Vitamin C respectively. The stems are generally 3-10 times lower in these concentrations than the leaves. The tubers have been found to contain the lowest levels of Vitamin C at 150 mg/kg (d.m.). Although the vitamin content of the tuber is much lower than that found in the leaves, it still exceeds values reported for potato tubers by approximately a factor of four. These results are highly dependent on the phase of development, climatic conditions and cultivation characteristics. 1.2.5. Moisture: Moisture content within the tuber and forage material is extremely dependent upon the irrigation and precipitation characteristics during cultivation of the crop. Due to the thin epidermal layer which surrounds the tuber, the Jerusalem artichoke is poorly protected against moisture loss. Thus, water content of the plant may represent only the current equilibrium between tubers and the surrounding soil. However, no evidence has been presented against the possibility that moisture content is pre-determined during tuber growth. Generally the level of moisture fluctuates closely at about 80% of the total tuber wet weight. The pH of the press juice obtained from the tubers is reported to be approximately 6.5. A number of organic acids have been identified in the juice, which include p-hydroxybenzoic acid, chlorogenic, vanillic, gentisic, p-coumaric, caffeic, and ferrulic acids. The relative levels of these Table 12: PR

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