John M. Grigor

Changes in phenolic compounds in Litchi (Litchi chinensis Sonn.) fruit during postharvest storage

Abstract Litchi (Litchi chinensis Sonn. cv. Huaizhi) fruit were stored at ambient temperature (20–25°C) for up to 7 days and at 4°C for up to 35 days for separation, purification and identification of individual phenolic compounds and investigation of their changes during postharvest storage. Results indicate that flavan-3-ol monomers and dimers were major phenolic compounds representing about 87.0% of the phenolic compounds that declined with storage or browning. Cyanidin-3-glucoside was a major anthocyanin and represented 91.9% of anthocyanins. It also declined with storage or browning. Small amounts of malvidin-3-glucoside were also found. Therefore, the major substrates for enzymatic oxidation were apparently flavan-3-ol monomers and dimers and cyanidin-3-glucoside.

The Role of Oral Processing in Dynamic Sensory Perception

Food oral processing is not only important for the ingestion and digestion of food, but also plays an important role in the perception of texture and flavor. This overall sensory perception is dynamic and occurs during all stages of oral processing. However, the relationships between oral operations and sensory perception are not yet fully understood. This article reviews recent progress and research findings on oral food processing, with a focus on the dynamic character of sensory perception of solid foods. The reviewed studies are discussed in terms of both physiology and food properties, and cover first bite, mastication, and swallowing. Little is known about the dynamics of texture and flavor perception during mastication and the importance on overall perception. Novel approaches use time intensity and temporal dominance techniques, and these will be valuable tools for future research on the dynamics of texture and flavor perception.

A comparative study of effects of nitrogen and argon on tyrosinase and malic dehydrogenase activities

Tyrosinase and malic dehydrogenase were treated with argon and nitrogen. Their activities were measured with time. The activities of tyrosinase and malic dehydrogenase when treated directly with argon, and when treated as a mixture of the enzymes and their substrates, were lower than with nitrogen treatments. The results suggest that argon reduces the activities of tyrosinase and malic dehydrogenase more than nitrogen. Tyrosinase activity with argon treatment was reduced by up to 14.2% more than nitrogen treatment when treated directly, and by up to 22.6% in the mixture of the enzyme and substrate. Malic dehydrogenase activity with argon treatment was reduced by up to 9.5% more than nitrogen treatment when treating the enzyme directly, and by up to 13.9% in the mixture of the enzyme and substrate.

Identification of proton type in concentrated sweet solutions by pulsed NMR analysis

The spin-spin proton relaxation times T2 of concentrated sucrose, maltose,D-glucose andL-proline solutions were determined using a Bruker Minispec NMR Spectrometer. Log spin echo amplitude decay curves were also determined and their non-linear nature allowed the proportions of different proton types to be calculated. These were in agreement with the theoretical proportions of ring (non-exchangeable protons), solute hydroxyl protons and water protons in the simple sugar molecules. A deuteration experiment confirmed that only non-exchangeable ring protons remained.

Changes in sensory perception of sports drinks when consumed pre, during and post exercise.

The aim of this study was to examine sensory perceptions towards different formulations of sports drinks when consumed before, at various points during, and following exercise. Following familiarization 14 recreational runners underwent four trials in a single blind counterbalanced design. Each trial utilised one of four different solutions: 7.5% carbohydrate, 421 mg L(-1) electrolyte (HiC-HiE); 7.5% carbohydrate, 140 mg L(-1) electrolyte (HiC-LoE); 1.3% carbohydrate, 421 mg L(-1) electrolyte (LoC-HiE) and water. Subjects were provided with 50-ml samples to ingest and then rate (using a 100-mm line scale) the intensity of sweetness, saltiness, thirst-quenching ability and overall liking before (-30 min), during (0, 30 and 60 min) and following (90 and 120 min) treadmill running exercise. Ratings of sweetness for all energy-containing drinks were higher during exercise relative to pre- and post-exercise conditions (P<0.05); ratings also increased with duration of exercise (P<0.001). Sweetness ratings for LoC-HiE increased during exercise (P<0.05) but remained the same for other beverages. Ratings of saltiness decreased for all energy-containing drinks during exercise relative to pre-exercise (P<0.05); ratings decreased with duration of exercise in these drinks (P<0.05). Ratings of thirst-quenching ability (P=0.039) and overall liking (P=0.013) increased with duration of exercise with all beverages. Significant changes in sensory perception occur when consuming sports drinks during exercise relative to non-exercise conditions. Temporal changes also occur during exercise itself which leads to enhanced liking of all beverages.

Analysis of Seafood Aroma/Odour by Electronic Nose Technology and Direct Analysis

Volatile aroma compounds are generally regarded to be important parameters for determining the flavour quality and spoilage index in marine-based products. Although sensory assessment is desirable (provided it is carried out scientifically and correctly) it has limitations, including the study of flavour at the molecular level. Therefore an increasing emphasis has been placed on developing instrumentation and methods which can reliably identify and rapidly quantify key odourants in seafood, and studying how processing, abuse and storage can affect them. This chapter describes the major chemical classes of flavour compounds found in seafood and the methods available for their detection.

Effect of Cooking on Consumers Perceptions of Mackerel (Scomber Scombrus) of Poor Quality

Wrapped and unwrapped raw mackerel samples, stored chilled (Chilled mackerel) and frozen then chilled (FC mackerel), were monitored for histamine content and assessed by sensory means over 3 days of storage. A score of about 20 coincided with the level at which fish were considered unacceptable by members of the panel. All samples showed good quality up to day 3 except unwrapped FC mackerel which showed fair quality. Cooked mackerel samples were also assessed during the same period for flavor, odor, texture and overall opinion about the effect of cooking on overall aroma quality. All samples showed normal flavor characteristics of good quality fish during storage. Although highly significant differences (P 0.05) were observed between the trials when the cooked mackerel samples were used. This indicated that cooking would appear to have masked any undesirable changes observed in fish, provided these changes were not extreme. Further investigation showed that cooking resulted in increases in the quantity of aldehydes detected. This might be crucial for overall aroma quality by masking some of the undesirable aroma changes in fish

The effect of collagenase, water and calcium chloride on the removal of Salmo salar (salmon) and Oncorhynchus mykiss (trout) pin bones

The aim of this study was to determine the influence of the fillet structure on the deboning force required to remove salmon and trout pin bones. Salmon and trout fillets with differing fillet structure were used, in order to study the importance of the fillet structure on the deboning process. In the first test naturally gaping and non-gaping fillets were compared. To confirm the role that the collagen plays within the fillet structure, the fillets underwent series of treatments. Fillets were put into (i) a collagenase solution to remove the collagen in the fillet and (ii) a calcium chloride solution to determine if collagen was the main influential factor. Both treated salmon and trout fillets were again compared to untreated fillets from the same batch. The results indicate that collagenase and calcium chloride have a large interaction on deboning force compared to water or no treatments.