Ingolf U. Grün

Antimicrobial and antioxidant activities of natural extracts in vitro and in ground beef.

Inhibition of Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes by grape seed extract (ActiVin) and pine bark extract (Pycnogenol) and the effect of these natural extracts on the oxidative stability of raw ground beef were studied. In an agar dilution test, the MICs of ActiVin and Pycnogenol were determined to be 4.0 mg/ml for 4.43 log CFU per plate of E. coli O157:H7 and 4.0 mg/ml for 4.38 log CFU per plate of L. monocytogenes. In an inhibition curve test, populations of E. coli O157:H7, Salmonella Typhimurium, and L. monocytogenes fell to below the detection limit (10 CFU/ml) after 16 h of incubation. The numbers of E. coli O157:H7, L. monocytogenes, and Salmonella Typhimurium declined by 1.08, 1.24, and 1.33 log CFU/g, respectively, in raw ground beef treated with 1% Pycnogenol after 9 days of refrigerated storage. ActiVin (1%) and oleoresin rosemary (1%) resulted in an approximately 1-log CFU/g reduction in the populations of all three pathogens after 9 days. The addition of 1% ActiVin and Pycnogenol contributed to the maintenance of an acidic pH of 5.80 and 5.58, respectively, in raw ground beef. Compared to the control, all treatments increased in L* (lightness), with the exception of ActiVin. ActiVin and oleoresin rosemary had the highest a* (redness) and b* (yellowness) values, respectively. ActiVin most effectively retarded lipid oxidation, followed by Pycnogenol. The results suggest that these natural extracts have potential to be used with other preservative methods to reduce pathogenic numbers, lipid oxidation, and color degradation in ground beef.

Changes in the Profile of Genistein, Daidzein, and Their Conjugates during Thermal Processing of Tofu†

Profiles of genistein, daidzein, genistin, daidzin, and their acetyl- and malonyl-beta-glycosides were determined in tofu as affected by temperature and time. Tofu was heated in water at 80, 90, and 100 degrees C for 0 (control), 10, 20, 30, and 40 min, and the contents of the isoflavones of interest were quantified using reversed-phase HPLC. Total isoflavone content decreased most likely due to leaching of isoflavones into the water. Because the content of the isoflavones of the genistein series was little affected by the treatments, the decrease in the total isoflavone content was almost exclusively due to a decrease of the daidzein series. Changes in the profile of the daidzein series suggest little decarboxylation of the malonylglycoside to the acetylglycoside, but considerable de-esterification of the malonyl- and acetylglycoside to the beta-glucoside. Strongly temperature dependent decreases of the aglycon suggest possible thermal degradation of daidzein in addition to losses due to leaching.

Application of GPA and PLSR in correlating sensory and chemical data sets

Abstract This paper discusses the application of various multivariate statistical procedures to understand the relationship between sensory and instrumental flavor profiles. Ice cream with varying fat levels was used as the vehicle for the flavor compounds in the experiment. Chemical and sensory flavor profiles were obtained by modified dynamic headspace analysis and descriptive analysis, respectively. Chromatographic peak areas of flavor-volatiles were used as the variables for the chemical data set. Initially, principal component analysis and canonical variate analysis were performed separately on the chemical and sensory data sets to explore the structure of each set. Flavor volatiles were then further studied to investigate their impact on the sensory profile of ice cream using general procrustes analysis and partial least squares regression analysis. The results from the two statistical analysis methods are compared and discussed. Additionally, the effect of log-transformation of chemical data on the overall chemical–sensory relationship was evaluated within each statistical method.

Quantitation of hexanal by automated SPME for studying dietary influences on the oxidation of pork

Automated headspace solid-phase micro-extraction gas chromatography (auto-HS-SPME-GC) was employed to determine the hexanal content of ground pork shoulders from pigs raised on a normal corn diet and a corn diet high in oil and monounsaturated fatty acids. This external standard method showed good linearity (R2=0.999) and acceptable reproducibility (rsd=6.7%). Samples were stored refrigerated under light and analyzed on days 0, 3, 5, 7 and 9. Although no significant differences were observed between treatments in hexanal concentration, color, odor, or thiobarbituric acid-reactive substances (TBARS) value, TBARS and hexanal values increased over time, which became significant on days 7 and 9 for TBARS and on day 9 for hexanal. TBARS and hexanal concentration were correlated with R2 values of 0.992 and 0.804 for the treatment and control group, respectively. Auto-HS-SPME-GC provided a rapid and convenient method for monitoring the hexanal content of raw ground pork. HS-SPME using Carboxen/PDMS stable flex fiber provided the required sensitivity, linearity and reproducibility for measurement of hexanal in the headspace of raw ground pork.

Nutrient and antinutrient content of an underexploited Malawian water tuber Nymphaea Petersiana (Nyika)

Uncooked/sun‐dried (UCSD) and boiled/freeze‐dried (BFD) flours of the Malawian water tuber Nymphaea petersiana (Nyika) were analyzed for selected nutrients and antinutrients. On a wet weight basis, the flours contained 8.1 and 8.0% crude protein; 0.8 and 1.0% crude fat; 12.0 and 13.0% dietary fiber; and 2.2 and 1.9% ash, respectively. The flours also contained 928 and 1300 μg/g of calcium; 2600 and 2200 μg/g of phosphorus; 88 and 20 μg/g of iron; and 22 and 20 μg/g of zinc, respectively. USCD and BFD flours were limiting in lysine and had amino acid scores of 91 and 84. The predominant fatty acids in the tubers were oleic (47%), linoleic (32%), palmitic (21%), and linolenic (7%). Tannin content was 1.5 and 1.0%; phytate content was 5.4 and 3.9 μg/g; trypsin activity was reduced from 400 to 55 TIU/g of tuber and chymotrypsin activity was reduced from 240 to 50 CIU/g by moist heat. Hydrogen cyanide levels were below detection limits (LOD < 16 nmoles/L) for both UCSD and BFD flour samples.