Hiroaki Yamauchi

Factors affecting the digestibility of raw and gelatinized potato starches.

The enzymatic digestibilities of raw and gelatinized starches in various potato starches, as well as sweet potato, cassava, and yam starches, were estimated, along with other starch properties, such as the phosphorus content, median granule size, and rapid visco analyzer (RVA) pasting properties. Furthermore, correlation coefficients were calculated between the hydrolysis rates (HR) by amylase and other starch quality parameters. A larger granule size was closely associated with a lower HR in raw starch, while the HR in gelatinized starch did not correlate with the median granule size. An increase in phosphorus content resulted in a definitely lower HR in raw starch and tended to decrease the HR in gelatinized starch for the composite of potato and other starches. In contrast, no correlation coefficients of the phosphorus content with the HRs in raw and gelatinized starches were observed within potato starches. Starches with higher peak viscosity and breakdown showed a lower HR in raw starch, while few or no effects of these RVA parameters on the HR in gelatinized starch were observed for the composite of potato and other starches or among potato starches, respectively.

Comparison of phenolic compositions between common and tartary buckwheat (Fagopyrum) sprouts

The phenolic compositions of non-germinated/germinated seeds and seed sprouts (at 6-10 day-old) of common (Fagopyrum esculentum Möench) and tartary (Fagopyrum tataricum Gaertn.) buckwheats were investigated. Phenolic compounds, including chlorogenic acid, four C-glycosylflavones (orientin, isoorientin vitexin, isovitexin), rutin and quercetin, were determined in the seed sprouts by high-performance liquid chromatography (HPLC). In the edible parts of common buckwheat sprouts, individual phenolics significantly increased during sprout growth from 6 to 10 days after sowing (DAS), whereas in tartary buckwheat sprouts they did not. While the sum contents of phenolic compounds in the edible part (mean 24.4mg/g DW at 6-10 DAS) of tartary buckwheat sprouts were similar to those of common buckwheat sprouts, rutin contents in the non-germinated/germinated seeds (mean 14.7mg/g DW) and edible parts (mean 21.8mg/g DW) of tartary buckwheat were 49- and 5-fold, respectively, higher than those of common buckwheat. Extracts of the edible parts of both species showed very similar free radical-scavenging activities (mean 1.7μmol trolox eq/g DW), suggesting that the overall antioxidative activity might be affected by the combination of identified phenolics and unidentified (minor) components. Therefore, buckwheat seed sprouts are recommended for their high antioxidative activity, as well as being an excellent dietary source of phenolic compounds, particularly tartary buckwheat sprouts, being rich in rutin.

Lactic acid fermentation of potato pulp by the fungus Rhizopus oryzae

Thirty-eight strains of the fungus Rhizopus oryzae were grown on potato pulp, an agricultural by-product of the starch industry. Either lactic acid or fumaric acid and ethanol were formed, and the ratio differed among the strains tested. The highest amount of L(+)-lactic acid (10 mg/g fresh matter) was observed in the pulp fermented for six days by Rhizopus oryzae IFO 4707. The IFO 4707 strain rapidly reduced the hardness and pH of potato pulp within one day followed by the gradual synthesis of lactic acid. A composition analysis showed that the enzymes secreted from the fungal cells hydrolyzed starch efficiently with partial degradation of the cell wall. Rhizopus oryzae may be used as an inoculant for ensiling potato pulp and other agricultural by-products containing starch.

Changes in sugar content and activity of vacuolar acid invertase during low-temperature storage of potato tubers from six Japanese cultivars

The storage of potato tubers at low temperatures leads to the accumulation of sugars in a process called “low-temperature sweetening.” To understand this phenomenon, we measured the sugar contents and the activity of acid invertase over several months in tubers of six Japanese cultivars stored at 4°C or 20°C. At 20°C , few changes in sugar contents took place in any of the tubers. On the other hand, when stored at 4°C, three types of changes were observed among the cultivars: (1) increased levels of reducing sugars during storage; (2) a pattern similar to that of type 1, but with 4- to 6-fold lower levels of reducing sugars throughout storage; and (3) increased sucrose, but not reducing sugars. The activity of vacuolar acid invertase increased in the type-1 cultivars, whereas, in the type-2 and type-3 cultivars, the activities were very low during storage at 4°C. Reverse transcription-polymerase chain reaction analysis of acid invertase showed that the transcripts of the enzyme accumulated in the tubers stored at 4°C in the type-1 cultivars but not in type-3. These results suggest that the activity of vacuolar acid invertase is related to the types of changes that occurred in sugar content during low-temperature storage among the potato cultivars.

Effects of Storage Temperature on the Contents of Sugars and Free Amino Acids in Tubers from Different Potato Cultivars and Acrylamide in Chips

To clarify the effects of storage temperature on potato components and acrylamide in chips, tubers from five cultivars were stored at various temperatures (2, 6, 8, 10, and 18 °C) for 18 weeks, and the contents of sugars, free amino acids in tubers, and acrylamide in chips after frying were analyzed. At temperatures lower than 8 °C, the contents of reducing sugars increased markedly in all cultivars, with similar increases in the acrylamide level and dark brown chip color. Free amino acids showed little change at the storage temperatures tested and varied within certain ranges characteristic of each cultivar. The contents of reducing sugars correlated well with the acrylamide level when the fructose/asparagine molar ratio in the tubers was <2. When the fructose/asparagine ratio was >2 by low-temperature storage, the asparagine content, rather than the reducing sugar content, was found to be the limiting factor for acrylamide formation.

Change in content of sugars and free amino acids in potato tubers under short-term storage at low temperature and the effect on acrylamide level after frying.

Changes in the sugar and amino acid contents of potato tubers during short-term storage and the effect on the acrylamide level in chips after frying were investigated. The acrylamide content in chips began to increase after 3 days of storage at 2 °C in response to the increase of glucose and fructose contents in the tubers. There was strong correlation between the reducing sugar content and acrylamide level, R2=0.873 for fructose and R2=0.836 for glucose. The sucrose content had less correlation with the acrylamide content because of its decrease after 4 weeks of storage at 2 °C, while the reducing sugar in potato tubers and the acrylamide in chips continued to increase. The contents of the four amino acids, i.e., asparatic acid, asparagine, glutamic acid and glutamine, showed no significant correlation with the acrylamide level. These results suggest that the content of reducing sugars in potato tubers determined the degree of acrylamide formation in chips. The chip color, as evaluated by L* (lightness), was correlated well with the acrylamide content.

Structural Elucidation of 4-(Cystein-S-yl)butyl Glucosinolate from the Leaves of Eruca sativa

The structurally unique glucosinolate (GSL), 4-(cystein-S-yl)butyl GSL, was identified in the leaves of hydroponically-grown rocket salad (Eruca sativa Mill.). Its electrospray ionization mass spectrometry (ESI-MS)/MS spectrum indicated that this unusual GSL had a molecular weight of 414 as a desulfo (DS)-GSL, and a molecular formula of C14H25N2O8S2 based on its negative ion matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) spectrum. For further confirmation, the 4-(cystein-S-yl)butyl DS-GSL was prepared with authentic L-Ser and purified dimeric 4-mercaptobutyl DS-GSL, and its chemical structure then confirmed by ESI-MS/MS data. It is named “glucorucolamine” as a trivial name from its ammonia sensitivity. This unique GSL was found to the greatest extent when rocket salad was grown in a 100% NH4 +-N nutrient solution. Despite it clearly seems to reduce the detoxification of excess NH4 + in the leaves of rocket salad, present knowledge about the unique GSL is still far from being sufficient.

Hepatoprotective Effects of Purple Potato Extract against D-Galactosamine-Induced Liver Injury in Rats

We investigated the hepatoprotective effect of purple potato extract (PPE) against D-galactosamine (GalN)-induced liver injury in rats. PPE (400 mg) was administered once daily for 8 d, and then GalN (250 mg/kg of body weight) was injected at 22 h before the rats were killed. Serum tumor necrosis factor alpha (TNF-α), lactate dehydrogenase (LDH), alanine aminotransferase (ALT), and asparate aminotranferase (AST) levels increased significantly after injection of GalN, but PPE inhibited GalN-induced alterations in serum TNF-α, LDH, ALT, and AST levels. Hepatic lipid peroxide and glutathione levels in the control + GalN group were higher and lower respectively than those in the control group, and those in the PPE + GalN group did not differ from that in the control group. The lipid peroxide level in hepatic microsomes treated with 2,2′-azobis (2-amidinopropane) dihydrochloride in the PPE group was significantly lower than that in the control group. This suggests that PPE has hepatoprotective effects against GalN-induced hepatotoxicity via inhibition lipid peroxidation and/or inflammation in rats.

Properties of Starches from Near-Isogenic Wheat Lines with Different Wx Protein Deficiencies

ABSTRACT To determine the effect of amylose content on the starch properties, the amylose content, pasting properties, swelling power, enzymatic digestibility, and thermal properties of partial and perfect waxy types along with their wild-type parent were analyzed. As expected, amylose content decreases differently in response to the loss of each Wx gene, showing the least response to Wx-A1a. Most of the characteristics, except the thermal properties of the amylose-lipid complex in differential scanning calorimetry (DSC), differed significantly among the tested types. Furthermore, the breakdown, setback, and pasting temperatures from the Rapid Visco Analyser (RVA) and the enzymatic digestibility, swelling power, peak temperature, and enthalpy of starch gelatinization from DSC showed a correlation with the amylose content. The relationships between the peak viscosity from the RVA and the onset temperature of starch gelatinization determined by DSC with amylose content of the tested materials were not clear...

Influence of Amylose Content on Cookie and Sponge Cake Quality and Solvent Retention Capacities in Wheat Flour

ABSTRACT Reduced amylose wheat (Triticum aestivum L.) produces better quality noodles and bread less prone to going stale, while little is known about the relationships between amylose content and the quality of soft wheat baking products such as sugar snap cookies (SSC) and Japanese sponge cakes (JSC). Near-isogenic lines developed from wheat cultivar Norin 61, differing in their level of granule-bound starch synthase (Wx protein) activity, were used to produce wheat grains and ultimately flours of different amylose contents. These were tested with regard to their effect on soft wheat baking quality and solvent retention capacities (SRC). Amylose content was strongly correlated to cookie diameter (r = 0.969, P < 0.001) and cake volume (r = 0.976, P < 0.001), indicating that the soft wheat baking quality associated with SSC diameter and JSC volume were improved by an incremental increases in amylose content. Among the four kinds of SRC tests (water, sodium carbonate, sucrose and lactic acid), the water SRC...