Daniel N. Sila

Effect of Temperature and High Pressure on the Activity and Mode of Action of Fungal Pectin Methyl Esterase

Pectin was de‐esterified with purified recombinant Aspergillus aculeatus pectin methyl esterase (PME) during isothermal‐isobaric treatments. By measuring the release of methanol as a function of treatment time, the rate of enzymatic pectin conversion was determined. Elevated temperature and pressure were found to stimulate PME activity. The highest rate of PME‐catalyzed pectin de‐esterification was obtained when combining pressures in the range 200–300 MPa with temperatures in the range 50–55 °C. The mode of pectin de‐esterification was investigated by characterizing the pectin reaction products by enzymatic fingerprinting. No significant effect of increasing pressure (300 MPa) and/or temperature (50 °C) on the mode of pectin conversion was detected.

Extraction and characterization of pectic polysaccharides from easy- and hard-to-cook common beans (Phaseolus vulgaris)

The occurrence of the hard-to-cook (HTC) defect in legumes is characterized by the inability of cotyledons to soften during the cooking process. This phenomenon may be influenced by pectin properties. The objective of this study was to characterize the pectic polysaccharides comprised in the alcohol insoluble residue (AIR) extracted from easy-to-cook (Rose coco) and hard-to-cook (Pinto) common beans. This would provide an insight in the relationship between the pectin properties and HTC defect. The AIR was extracted from raw, half-cooked hard, half-cooked soft and fully-cooked bean samples. Subsequently, it was fractionated into water-, chelator- and Na2CO3-soluble pectin fractions and a hemicellulose fraction. For the AIR and the pectin fractions, determination of the galacturonic acid content, neutral sugars, degree of methylesterfication (DM), degree of acetylation (DAc) and molar mass (MM) distribution was performed. Results on the pectin fractions, MM distribution and pectin content profile, revealed that Rose coco pectin generally showed higher pectin solubility than Pinto. Neutral sugar profiles indicated that Pinto contained higher amounts of branched pectin (i.e. arabinans) than Rose coco. There was no difference between the DM of Pinto and Rose coco, however, the DAc was higher in Rose coco. In conclusion, the differences in pectin structure and solubility properties between easy- and hard-to-cook common beans might contribute to the differences in their cooking behavior.

Detailed analysis of seed coat and cotyledon reveals molecular understanding of the hard-to-cook defect of common beans (Phaseolus vulgaris L.).

The hard-to-cook (HTC) defect in legumes is characterized by the inability of cotyledons to soften during the cooking process. Changes in the non-starch polysaccharides of common bean seed coat and cotyledon were studied before and after development of the HTC defect induced by storage at 35°C and 75% humidity for 8months. Distinct differences in the yields of alcohol insoluble residues, degree of methoxylation (DM), sugar composition, and molar mass distribution of non-starch polysaccharides were found between the seeds coat and cotyledons. The non-starch polysaccharide profiles, both for seed coats and cotyledons, significantly differed when comparing HTC and easy-to-cook (ETC) beans. In conclusion, differences in the structure, composition and extractability of non-starch polysaccharides between the ETC and HTC beans confirmed the significant role of pectin polysaccharides in interaction with divalent ions in the HTC development, which consequently affect their cooking behaviors.

High pressure processing to optimise the quality of in-pack processed fruit and vegetables.

Publisher Summary This chapter highlights that High Pressure (HP) technology has been known for more than 100 years, but was adopted and adapted for industrial food applications in the early 1990s. HP processing at room/moderate temperature has been introduced for industrial food processing and preservation. Currently, in countries such as Japan, United States, Spain, France, Czech Republic and United Kingdom, this technique is being applied to produce high-quality foods, including ham, sea food, jam, mixed fruit and vegetables, juices and sauces, etc. Typically, foods are pre-packed in flexible containers or in plastic packs before HP treatment. Small molecules, such as vitamins, pigments, and volatile compounds, are less affected by HP processing compared with proteins/enzymes, which are often characterized by a complex three-dimensional architecture stabilized by various covalent and non-covalent interactions. Consequently, HP processing allows the processing of foods while preserving their “fresh-like” properties, due to the limited loss of flavor, color, and nutritional value. From an engineering point of view, HP processing is faced with limitations of heat transfer, although it applies pressure isostatically, that is, instantaneously and uniformly throughout a mass of food material irrespective of size, shape, and composition. HP processing has been extended, on a laboratory scale, to applications at elevated temperatures, referred to as High Pressure Sterilization (HPS) to obtain spore inactivation. This application takes advantage of adiabatic heating during pressurization.