Guanghua Zhao

Characteristics of Thin-Layer Infrared Drying of Apple Pomace With and Without Hot Air Pre-drying

Thin-layer infrared drying characteristics of apple pomace, with and without hot air pre-drying, were studied with a laboratory scale infrared dryer. Moreover, ten commonly used mathematical models were used to fit experimental data. Logarithmic model and Page model were most adequate in describing thin-layer drying of fresh and pre-treated apple pomace respectively. The values of average effective diffusivity in drying the pre-treated apple pomace were about 1.3 times of that in the fresh apple pomace with the initial moisture content of 40% (wet basis).The values of activation energy of moisture diffusion were about 30 kJ/mol for the fresh and pre-treated apple pomace respectively. Infrared drying, combined with hot air pre-drying, can save 20% of drying time to remove the same amount of remained moisture as compared to the infrared drying alone. The above findings might be used for operation of drying apple pomace.

Physicochemical Characteristics of Orange Juice Samples From Seven Cultivars

Some physicochemical parameters of orange juice from seven orange varieties (Pineapple orange, Hamlin, Trovita, Jincheng, 1232 Tangor, Olinda Valencia, and Delta Valencia) were analyzed, special attention was paid to the level of sugars, organic acids, free amino acids, mineral composition, and color parameters. The results showed that total soluble solids (TSS), TSS/titratable acidity (TA) ratios, sugars, and organic acids were kept within a proper range for juice processing except that Jincheng had lower TSS than the others. Sucrose was the most dominant sugar in the orange cultivars, followed by fructose and glucose, while citric acid was the principal organic acid. Serine and proline were the principal amino acids. Potassium was the most abundant mineral in all of the juice samples, followed by magnesium and calcium. The sodium content of most varieties was under 10 mg kg−1. Though all of the samples had orange colour, Olinda Valencia and Delta Valencia had deeper red colour than the others. Statistically significant differences (P<0.05) were found between the samples in most of the characteristics. The results provided important information on the physicochemical characteristics of the varieties and on how to make the best use of orange cultivars for different purposes, which is of significance for both technological research and processing practice.

Survey of acrylamide levels in Chinese foods

A survey of levels of acrylamide (AA) in 349 food products obtained from the Chinese market was conducted. AA was determined by an liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. The limit of detection (LOD) and the limit of quantification (LOQ) of the method in four different matrices ranged from 0.8 to 10 µg kg−1 and from 4.0 to 25 µg kg−1, respectively. The results from this survey indicated that AA was present in all samples except drinking water and tea. AA contents in different samples varied greatly according to the raw materials and processing conditions. The highest level of AA was found in potato products, with an average level of 1467 µg kg−1. Preliminary estimates of AA exposure and risk assessment of AA from foods in the Chinese population were performed using a combination of data obtained in the present survey and 2002 dietary consumption survey carried out in 2002 for the Chinese population. The average dietary exposure of AA was estimated to be 0.38 µg kg−1 body weight day−1, which is relatively low compared with the result reported by the Food and Agricultural Organization/World Health Organization (FAO/WHO). Furthermore, the margin of exposure for neurotoxicity, reproductive toxicity, and carcinogenicity of AA was calculated to be 1318, 5250, and 787, respectively.

Effect of tannic acid on properties of soybean (Glycine max) seed ferritin: a model for interaction between naturally-occurring components in foodstuffs.

There are many components with different properties co-existing in food, so interactions among these components are likely to occur, thereby affecting food quality. However, relatively little information is available on such interactions. In this study, we focus on the interaction between tannic acid (TA) and soybean seed ferritin (SSF), since they co-exist in many foodstuffs, and the consequence of this interaction. As expected, TA interacts with SSF, resulting in changes in the tertiary/quaternary structure of the protein, while having no effect on its primary and secondary structure. On one hand, such interaction leads to protein association, which markedly inhibited ferritin degradation by pepsin at pH 4.0 and trypsin at pH 7.5. On the other hand, iron release was faster with TA than with ascorbic acid, and such release has a negative effect on iron supplementation. These results help to understand the interactions of food components.

The Effect of Freezing Modes and Frozen Storage on Aroma, Enzyme and Micro-organism in Hami Melon

The effects of freezing modes and time in frozen storage on aroma, enzymes and micro-organisms in Hami melon, also called cantaloupe melon (Cucumis melo. var. reticulatus Hami melon), were determined. Freezing process and frozen storage could not significantly reduce either micro-organisms counts or the enzymatic activities of polyphenoloxidase (PPO), peroxidase (POD) and lipoxidase (LOX) in melon. Liquid nitrogen ultra-rapid freezing maintained most aromatic components of the melon as compared with slow freezing. The mechanism of aromatic change in frozen melon was mainly ascribed to esters changing continuously in variety and concentration because of enzymolysis or synthetic reactions of esters catalysed by LOX. Meanwhile, increasing concentration of linoleic acid and linolenic acid in frozen melon cells promoted the biochemical reaction of unsaturated fatty acids in LOX system, so that enzymolysis of the double bonds in the ninth and tenth carbon of linoleic acid and linolenic acid was accelerated. Consequently, with the prolongation of time in frozen storage more and more unsaturated alcohols and aldehydes with 6 and 9 carbons were produced, the green notes of frozen storage melon became more and more intense, and the ester fragrance became more and more feeble. The above findings can benefit the development of cantaloupe melon process industry.

Correlation of methylglyoxal with acrylamide formation in fructose/asparagine Maillard reaction model system.

α-Dicarbonyl compounds were highly reactive intermediates formed in Maillard reaction (MR), and o-phenylenediamine (OPD) was widely used as a trapping agent for α-dicarbonyl compounds. Both aqueous fructose/asparagine (Fru/Asn) and fructose/asparagine/o-phenylenediamine (Fru/Asn/OPD) model systems were heated at 150°C for up to 30min. Methylglyoxal (MG) was the main α-dicarbonyl compounds formed in MR, which was chosen as a representative of α-dicarbonyl compound to investigate the influence on acrylamide (AA) formation. The concentrations of AA, MG and Asn were detected during MR by HPLC method. The results indicated that the formation of AA increased with the heating time, and nearly 75% of AA was formed through the participation of α-dicarbonyl compounds. The amounts of formation and consumption of MG increased with heating time, and from 12min of reaction, the consumed amounts of MG accounted for 62.1-90.3% on the basis of total amounts of MG formed in MR, suggesting that most of the MG took part in further reactions. Meanwhile, Asn concentration decreased with heating time in both models. The formation of AA and consumption of Asn were highly correlated with MG. Indeed, as MG concentration in MG/Asn model system decreased during heating at 150°C, the concentration of AA significantly increased. The coefficient of correlation between consumed amounts of MG and the formed amounts of AA was 0.931, demonstrating that MG plays a role in AA formation.

The interaction of DNA with phytoferritin during iron oxidation.

Phytoferritin from legume seeds is considered an iron supplement with great potential. Phytoferritin co-exists with plastid DNA in amyloplasts of legume seed cells where Fe(2+) is oxidized into Fe(3+), followed by storage within the inner cavity of the protein. In this study, the interaction of plasmid DNA with black bean (Phaseolus vulgaris L.) seed ferritin (BSF) during iron oxidation was studied. Results indicated that iron ions facilitated formation of apoBSF aggregates at a high iron loading (>48 Fe(2+)/shell). Interestingly, the co-existence of DNA and ferritin has a pronounced effect on iron uptake by ferritin. This view is confirmed by a pronounced increase in the rate of iron oxidation catalysed by apoBSF in the presence of DNA. On the other hand, the apoBSF exhibited a marked DNA-protective function against oxidative damage at a low loading of Fe(2+) (⩽ 48 Fe(2+)/shell). However, outside this ratio, such an effect gradually decreased, because the added iron exceeded the iron binding capacity of ferritin. The current study advances the understanding of the interaction among multi-components in foodstuffs.