Pectins in Processed Fruits and Vegetables: Part III—Texture Engineering

ABSTRACT: Current interest in controlling the textural and rheological properties of processed fruit and vegetable products has stimulated research on the biochemistry of the cell wall, with particular reference to pectin and its degradation. This review covers the literature over the last decade with respect to pectin engineering in the field of fruit and vegetable processing. Several applications, illustrating that refined manipulation of chemical and/or enzymatic pectin degradation can be used as a tool to improve the texture/rheology of thermally processed and frozen fruit and vegetable products, are described. The discussion includes an evaluation of the role of novel technologies such as high‐pressure processing in pectin engineering of processed fruits and vegetables. Furthermore, the possible role of pectin‐related enzymes other than pectin methylesterase (PME) and polygalacturonase (PG) and of the nontraditional, ferulic acid‐mediated cross‐linking process is discussed. Finally, new trends, challenges, and suggestions for future pectin engineering research are covered in this review.     

Pectins in Processed Fruits and Vegetables: Part II—Structure–Function Relationships

ABSTRACT: Pectin represents a very heterogeneous biopolymer whose functionality remains largely puzzling. The link between the pectin fine structure and functional properties with relevance to plant growth and development, as well as food processing, is continually being explored. This review describes the current knowledge of pectin structure–function relationships. Key mechanisms dictating pectin structure–function relationships are discussed, including the polymer biosynthesis, cross‐linking mechanisms, enzymatic and nonenzymatic conversion reactions, solubility properties, and more. Insight into the polymer structure–function relationships is highlighted by examining traditional and advanced methodologies used in pectin research. The role of pectin in modulating the quality characteristics of plant‐based foods is underlined while pin‐pointing some of the main challenges and perspectives. An integrated approach using the pectin structure–function relationship in the precision engineering of mechanical properties of tissue‐based systems is proposed.     

Fiber Contents of Selected Raw and Processed Vegetables, Fruits and Fruit Juices as Served

Pectin and neutral detergent fiber (NDF) contents were investigated for commercially processed foods as served: 10 vegetables, 10 fruits, and 8 fruit juices. Fiber content of fruits ranged from 0.7%?4.5% NDF and 0.28%?0.48% pectin; juices ranged from 0.1%?0.22% NDF and 0.2%?0.39% pectin. Fiber in frozen, canned and cooked vegetables ranged from 1%?4.4% NDF and 0.5%?1% pectin. In general, there is no evidence that any of the food preparation methods was superior. There appears to be no great loss of fiber when food is prepared by typical home methods or commercial processing.     

DIACETYL—A REVIEW: PART I—ANALYTICAL AND BIOCHEMICAL CONSIDERATIONS: PART II—BREWING EXPERIENCE

Diacetyl and 2,3-pentanedione are normal products of yeast metabolism and are formed in every brewery fermentation. The desired level in the final beer depends on the particular flavour aimed for but, in all types of beer, flavour defects are caused by excessive concentrations of diacetyl and many brewers might be happy to have no diacetyl in the beer. Recent improvements in analytical techniques show that many of the problems associated with diacetyl are due to the occurrence of compounds which can give rise to diacetyl in the finished beer. These compounds include the so-called “precursor,” acetolactic acid, but possibly other compounds such as the bisulphite addition compound of diacetyl are also involved. Study of the factors affecting diacetyl formation and removal by yeast shows how the concentration of diacetyl in beer can be controlled, and the processes at present used to regulate the diacetyl concentration in beer are described. The yeast strain used, the condition of the pitching yeast, the wort composition, the detailed management of the fermentation and the treatment of the beer during packaging and storage can all affect the diacetyl content of the beer.     

β-Carotene and Ascorbic Acid Retention in Fresh and Processed Vegetables

Broccoli, carrots, and green beans (grown in 2 consecutive years) were randomly divided into 3 treatments: fresh-refrigerated (F-R), frozen (FZ) or canned (C) (carrots only). FZ or C vegetables were processed within 24 h and stored for up to 1 yr. F-R vegetables were held at 4 °C for 3 wk (broccoli and green beans) or 6 mo (carrots). Trans b-carotene (Tb-C) and total ascorbic acid (AA) were determined at specified times, before and after microwave cooking. Vitamin content differed between years due to environmental conditions. Blanching resulted in AA loss, but retention remained stable after freezing broccoli and green beans. F-R green beans lost >90% AA after 16 d storage. Linear decreases in AAwere found in most F-R or FZ vegetables. Tb-C decreased slightly during freezer storage. Reductions in Tb-C occurred in canned carrots. Microwave cooking had minimal effects on AA or Tb-C.     

Processed Tart Cherry Products—Comparative Phytochemical Content,in vitro Antioxidant Capacity and in vitro Anti‐inflammatory Activity

Abstract: Processing of fruits and vegetables affects their phytochemical and nutrient content. Tart cherries are commercially promoted to possess antioxidant and anti‐inflammatory activity. However, processing affects their phytochemical content and may affect their related health benefits. The current study compares the in vitro antioxidant capacity and anti‐inflammatory cyclooxygenase activity of processed tart cherry (Prunus cerasus) products—cherry juice concentrate, individually quick‐frozen cherries, canned cherries, and dried cherries. Cherry products were analyzed for total anthocyanin and proanthocyanidin content and profile. On a per serving basis, total anthocyanins were highest in frozen cherries and total proanthocyanidins were highest in juice concentrate. Total phenolics were highest in juice concentrate. Juice concentrate had the highest oxygen radical absorbance capacity (ORAC) and peroxynitrite radical averting capacity (NORAC). Dried cherries had the highest hydroxyl radical averting capacity (HORAC) and superoxide radical averting capacity (SORAC). Processed tart cherry products compared very favorably to the U.S. Dept. of Agriculture‐reported ORAC of other fresh and processed fruits. Inhibition of in vitro inflammatory COX‐1 activity was greatest in juice concentrate. In summary, all processed tart cherry products possessed antioxidant and anti‐inflammatory activity, but processing differentially affected phytochemical content and in vitro bioactivity. On a per serving basis, juice concentrate was superior to other tart cherry products. Practical Application: Processing of fruits and vegetables affects their chemical and nutrient content and perhaps their related health benefits. Comparative studies are valuable to ascertain the effects of processing on fruit and vegetable chemical content and bioactivity. Here we present tart cherries as a model for this type of detailed comparison.     

果蔬冻藏工艺研究

着重探讨了果蔬冻结贮藏，原原料的选择、预处理、烫漂、冻结、包装、运输中注意的问题和对菠菜、青椒、青刀豆、菜花、早莓、西瓜的冻藏工艺进行了研究．     

Recent Development in Osmotic Dehydration of Fruit and Vegetables: A Review

Osmotic dehydration of fruits and vegetables is achieved by placing the solid/semi solid, whole or in pieces, in a hypertonic solution (sugar and/or salt) with a simultaneous counter diffusion of solutes from the osmotic solution into the tissues. Osmotic dehydration is recommended as a processing method to obtain better quality of food products. Partial dehydration allows structural, nutritional, sensory, and other functional properties of the raw material to be modified. However, the food industry uptake of osmotic dehydration of foods has not been extensive as expected due to the poor understanding of the counter current flow phenomena associated with it. However, these flows are in a dynamic equilibrium with each other and significantly influence the final product in terms of preservation, nutrition, and organoleptic properties. The demand of healthy, natural, nutritious, and tasty processed food products continuously increases, not only for finished products, but also for ingredient to be included in complex foods such as ice cream, cereals, dairy, confectionaries, and bakery products.     

果蔬渗透脱水技术研究进展

围绕影响渗透脱水效果及脱水过程中物质迁移的主要因素、促进物质迁移的方法、渗透脱水联合其它干燥技术对产品品质和能耗的影响等方面,对国内外果蔬渗透脱水技术的研究进展进行了综述,指出目前研究中存在的问题,并就未来的发展前景进行了展望.     

Elemental Analysis of Fruit and Vegetables from Tonga

Twelve foods from islands in the South Pacific Kingdom of Tonga were analyzed for eleven elements by plasma emission spectrometry. The foods were green banana, ripe banana, breadfruit, cassava, coconut, mango, pawpaw, plantain, sweet potato, the taros Talo Fatuna and Talo Tonga, and Pacific yam. The elements determined were Ca, K, Mg, P, S, B, Cu, Fe, Mn, Na and Zn. There were large differences between foods in their content of Ca, Cu, Fe, Mn and Na.     

Comparison of Sodium and Sodium/Potassium Salt Mixtures in Processed Vegetables

Green beans and torn were heat processed with different concentrations of a salt mixture as a sodium chloride (NaCl) substitute. The sodium (Na) and potassium (K) concentrations of the finished product were deter mined as well as the flavor desirability by an untrained panel. Certain levels of the salt mixture were judged not significantly different in desirability from the reference which contained 1.5% NaCl. The use of an equal mixture of NaCl and KCl was effective in improving the Na/K ratio.     

Operational Stability and Kinetic Study of a Membrane Reactor with Pectinases from Aspergillus niger

ABSTRACT: The kinetic and operational behavior of a free enzyme membrane reactor (FEMR) were analyzed. High conversion (83%) of the pectin could be achieved with a substrate-to-enzyme ratio of 23.3 at 46°C and pH 4.8, with a transmembrane pressure of 34.5 kPa and recycling flow rate of 36 L/h. The FEMR showed a 1st-order deactiva-tion profile with a calculated half life (t_1/2) of 21.7 d in the operation conditions. Akinetic study of the hydrolysis of pectin by free endopectinases from Aspergillus niger was done by the simultaneous use of a stirred-tank reactor and a FEMR. Kinetic data were fit to a model based on the Michaelis-Menten rate expression and the design equation for a continuous membrane reactor. The kinetic characteristics observed in the hydrolysis of pectin included a product competitive inhibition. The K_m and K_i values for the membrane reactor were 2 to 3 times greater those obtained in a stirred-tank reactor. On the basis of the V_max values, the configuration of the FEMR was found to have excellent catalytic efficiency when compared with the stirred-tank reactor.     

Ethylene Absorbent to Maintain Quality of Lightly Processed Fruits and Vegetables

Ethylene had an undesirable effect on the quality of kiwifruits, bananas, broccoli, and spinach leaves that were prepared and stored as lightly processed products. A 2.or 20 ppm ethylene treatment hastened the softening of the pulp of kiwifruits and bananas held at 20°C. Use of charcoal with palladium chloride, as ethylene absorbent, prevented the accumulation of the ethylene and was effective in reducing the rate of softening in kiwifruits and bananas and of chlorophyll loss in spinach leaves, but not in broccoli.     

HPLC Separation of Cis-Trans Carotene Isomers in Fresh and Processed Fruits and Vegetables

Resolution of cis-trans alpha- and beta-carotene isomers was achieved using a rapid (30 min) high-performance liquid chromatography method employing a slurry-packed calcium hydroxide column. The isomers found in fruit and vegetable products were identical to those formed through iodine catalyzed isomerization of carotene solutions. A survey of fresh and commercially processed fruit and vegetable products indicated that the greatest percentage of isomers was found in processed foods (20.1–54.0%). Of the fresh products surveyed, cis-isomers were found in plums, nectarines and peaches, and no cis-isomers were detected in sweet potatoes, carrots and tomatoes; however, all fresh green vegetables contained from 19.6–28.3% monocis-isomers.     

Effect of Temperature on Firmness of Thermally Processed Fruits and Vegetables

The firmness of many commercially canned fruits and vegetables was measured by puncture, extrusion and Texture Press over the temperature range3–48°C. The firmness almost always decreased with increasing temperature and the firmness-temperature plots were rectilinear. The firmness-temperature coefficient (FT) is defined as the percent change in firmness per degree temperature increase. It ranged from close to zero to about -1.0% for most of the samples tested. The temperature should be kept within narrow limits when making firmness measurements on thermally processed fruits and vegetables, otherwise significant errors can be introduced.     

绿色蔬菜加工中叶绿素金属离子络合物的研究进展

概述了绿色蔬菜在加工、储藏过程中叶绿素降解的可能机理和途径,探讨了叶绿素及其降解产物本身、金属离子及其浓度、叶绿素酶、pH值、加热温度和时间、表面活性剂等因素,对形成叶绿素金属离子络合物的影响.     

Cellulose, Hemicellulose and Lignin Content of Raw and Cooked Processed Vegetables

The NDF, ADF, cellulose, hemicellulose and lignin contents of five frozen vegetables (raw and boiled) and five canned vegetables (two of them fried) have been studied. In general, it was observed that boiling resulted in an increase in the NDF, ADF and cellulose content. There was also a slight increase in hemicellulose values. The lignin contents of most vegetables did not change upon boiling. When the cooking process was frying, a drastic decrease of NDF, ADF, cellulose, and lignin contents occurred, while the amount of hemicellulose changed slightly in the vegetables analyzed.     

Amylase Activity in Banana Fruit: Properties and Changes in Activity with Ripening

Following subcellular fractionation and centrifugation, the amylase activity was located in the cytosol fraction of banana fruit. Over 80% of the observed activity (15—20 units per mg of protein) was attributed to α-amylase. The activity of β-amylase was tenfold lower and starch phosphorylase activity was low (17 μg inorganic phosphorus released per mg protein per 24 hr.). The activity of amylase in crude preparations was stimulated 40% by calcium ions. The amylase preparation, which was very stable at 4°C, hydrolyzed soluble potato starch and banana starch at similar rates. Maximum activity was observed between pH 6—7. The energy of activation of hydrolysis was 9.74 Kcal/mole. Amylase was quite active up to 62°C but rapidly lost activity above this temperature. There was an approximate twofold increase in amylase during the initial phase of ripening.