In the present study, we identified several food-derived collagen peptides in human blood after oral ingestion of some gelatin hydrolysates. Healthy human volunteers ingested the gelatin hydrolysates (9.4-23 g) from porcine skin, chicken feet, and cartilage after 12 h of fasting. Negligible amounts of the peptide form of hydroxyproline (Hyp) were observed in human blood before the ingestion. After the oral ingestion, the peptide form of Hyp significantly increased and reached a maximum level (20-60 nmol/mL of plasma) after 1-2 h and then decreased to half of the maximum level at 4 h after the ingestion. Major constituents of food-derived collagen peptides in human serum and plasma were identified as Pro-Hyp. In addition, small but significant amounts of Ala-Hyp, Ala-Hyp-Gly, Pro-Hyp-Gly, Leu-Hyp, Ile-Hyp, and Phe-Hyp were contained.

Type V collagen became solubilized in softened sardine muscle after 1 day of chilled storage with the concomitant weakening of pericellular connective tissue induced by disintegration of thin collagen fibrils. However, no significant changes were observed in the structure of interstitial connective tissue or biochemical properties of type I collagen. Z disk in myofibrils showed structural changes, but no significant loss of longitudinal continuity of myofibrils was observed even at the deteriorated Z disk from the muscle destroyed by compression test. On the other hand, tiger puffer muscle did not show significant softening during the storage, with no significant changes in structure of connective tissues and biochemical properties of collagens. These facts suggest that degradation of type V collagen causes disintegration of the thin collagen fibrils in pericellular connective tissue, weakening pericellular connective tissue and resulting in postharvest softening. Keywords: Collagen; postharvest storage; fish; connective tissue; muscle; collagen V

Post-mortem changes of types I and V collagens in rainbow trout muscle were examined in relation to the softening of fish muscle during chilled storage. Degradation of helical regions of collagens was not detected. On the other hand, the solubility of type V collagen increased significantly, while that of type I collagen did not change. These facts suggest that degradation of nonhelical regions or intermolecular cross-links occur preferentially in type V collagen.

The antimutagenic activity of n-hexane extracts from eight strains of daikon (Raphanus sativus; Japanese white radish) have been examined using the UV-induced mutation assay of Escherichia coli B/r WP2. A correlation was found between the potency of antimutagenicity and the amount of 4-(methylthio)-3-butenyl isothiocyanate (MTBITC) in their n-hexane extracts. Because the pure MTBITC also showed antimutagenicity, MTBITC is presumably the active antimutagen principle in n-hexane extracts of daikon. Among the eight strains of daikon studied, Aokubi, the improved common strain in Japan, contained 71.0 micromol of MTBITC in 100 g of fresh daikon. In contrast, Karami and Momoyama, which are original wild strains, contained much more MTBITC (363.5 and 168.0 micromol/100 g, respectively). In addition, phenethyl isothiocyanate was found in a lesser amount (5-33 nmol/100 g) in eight strains of daikon, and allyl isothiocyanate and benzyl isothiocyanate were not detectable in any strains (<3 nmol/100 g). The amount of total isothiocyanate in grated daikon was 7.0 times higher than that in cut daikon measured after 30 min of cooking. Through eating habits, humans might be able to consume substantial amounts of the antimutagen MTBITC from dishes using the grated form of wild strains of daikon. Therefore, it is possible to substantially increase the intake of the antimutagenic ingredient of daikon (i.e., MTBITC) by changing food preferences and preparation procedures (i.e., using the grated form of the wild strains).

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Myrosinase is a cytosolic plant enzyme present in daikon ( Raphanus sativus, Japanese white radish) roots that hydrolyzes 4-methylthio-3-butenyl glucosinolate (MTBGLS) into the natural pungent agent 4-methylthio-3-butenyl isothiocyanate (MTBITC), which possesses antimicrobial, antimutagenic, and anticarcinogenic properties. The concentration of MTBGLS, myrosinase activity, and production of MTBITC in seven daikon varieties (one conventional and six heirlooms) were determined to rank the activity of the glucosinolate-myrosinase system and identify critical factors influencing the production of MTBITC. The six heirloom varieties produced 2.0-11.5 times higher levels of MTBITC as compared to the conventional variety, Aokubi, which is consumed by the present Japanese population. The myrosinase was located exclusively in the outer epidermal layer in Aokubi, and MTBGLS was widely distributed throughout the root tissue. Although the skin is a potentially rich source of myrosinase in Aokubi, the skin is usually peeled off in the current practice of preparing daikon for cooking. New practices are therefore proposed for the preparation of daikon tubers that eliminate the peeling of the skin to avoid removing the enzyme needed to convert MTBGLS to the health-beneficial MTBITC. It is also concluded that the consumption of heirloom daikon varieties in addition to changes in food preparation will optimize the health benefits of daikon.

Peptides in the protease digests of some acidic and basic proteins in the range of 0.1−1.0% (w/v) could be fractionated with high reproducibility by a preparative isoelectric focusing on the basis of the amphoteric nature of samples in the absence of added carrier ampholytes. Enrichment of peptides of up to 15-fold could be achieved by the present method. This technique, referred to as autofocusing, did not require or yield any toxic solvents or solutes; thus, the present approach can be a low-cost and biocompatible method for peptide fractionation. Keywords: Peptide; peptide fractionation; preparative isoelectric focusing; electrophoresis