Effects of fatty acid and emulsifier on the complex formation and in vitro digestibility of gelatinized potato starch

The effects of fatty acid, monoacylglycerol, and polyglycerol fatty acid ester with varying chain length in their acyl chains on the extent of complex formation (complex index) and in vitro enzymatic digestibility of gelatinized potato starch were investigated. The complex index increased with increase in the concentration of the ligands (fatty acid, monoacylglycerol, and polyglycerol fatty acid ester), with the plateau in the complex index value depending on the type of ligands. In comparison of complex index among fatty acid-samples, the complex index maximum increased as the chain length increased up to octanoic acid and then decreased. In comparison of complex index among fatty acid-, monoacylglycerol-, and polyglycerol fatty acid ester-samples at each acyl chain, the complex index maximum followed the order polyglycerol fatty acid ester > monoacylglycerol > fatty acid. Fatty acid, monoacylglycerol, and polyglycerol fatty acid ester with long acyl chains greatly reduced the enzymatic hydrolysis of starch. Polyglycerol fatty acid ester with palmitic acid chains was the strongest inhibitor of starch hydrolysis, suggesting that further complex formation may occur during the hydrolysis of gelatinized starch (enzyme-annealing).     

Equations for spectrophotometric determination of relative concentrations of myoglobin derivatives in aqueous tuna meat extracts

The percentage of metmyoglobin (%metMb) in aqueous meat extracts of bigeye and bluefin tuna and beef samples were estimated using previously reported equations derived from the absorption spectra of horse Mb. The results demonstrate that in an aqueous extract, the difference in %metMb estimated by the different equations was negligible for beef samples. Conversely, in an aqueous tuna extract, different %metMb values were obtained with the different equations. The discrepancy in the tuna sample results might be due to differences in absorption spectra for horse and tuna Mb. Therefore, a new set of equations derived from the absorption spectra of bigeye tuna Mb, reported by Matsuura and Hashimoto (1955), was established. The accuracy of the proposed equations was compared with the cyanmetmyoglobin (cyanmetMb) method. The results show that the total Mb concentrations estimated by our proposed equations were in good agreement with the results obtained by the conventional cyanmetMb method (R² = 0.984). Therefore, the new set of proposed equations is valid for the spectrophotometric determination of the relative proportions of Mb derivatives and total Mb concentration in aqueous tuna meat extracts.     

Quantitative measurement of metmyoglobin in tuna flesh via electron paramagnetic resonance

The potential of electron paramagnetic resonance (EPR) spectroscopy in the quantitative determination of metmyoglobin (metMb) in tuna flesh was examined and compared with conventional visible spectrophotometry (VIS). Both fresh and stored tuna samples were directly subjected to EPR measurement at −150 °C without pigment extraction, and their metMb concentrations ([metMb_TUNA]_EPR) were determined from a calibration curve. A linear calibration curve with good correlation (R² = 0.987) was obtained by a plot between EPR intensities and the known [metMb_CALI]_VIS concentrations, where [metMb_CALI]_VIS is the concentration of metMb obtained from visible spectrophotometry for the stock metMb solution. The results show that differences between [metMb_TUNA]_EPR and [metMb_TUNA]_VIS for tuna meats are negligible at low concentrations of metMb. However, [metMb_TUNA]_EPR tends to be higher than [metMb_TUNA]_VIS at a higher concentration of metMb. This is probably due to incomplete pigment extraction from tuna samples that have been stored for a long period of time. This results in experimental inaccuracy of [metMb_TUNA]_VIS at higher concentrations of metMb. The overall results suggest that the EPR method is a suitable technique for quantitative measurement of metMb in tuna meat without pigment extraction. Since the EPR method operates at −150 °C, this technique could also be very useful in determining the metMb content in frozen tuna meat during low-temperature storage without thawing.