Tri-trophic effects of transgenic insect-resistant tobacco expressing a protease inhibitor or a biotin-binding protein on adults of the predatory carabid beetle Ctenognathus novaezelandiae.

Tri-trophic impacts on adult predatory carabid beetles, Ctenognathus novaezelandiae, of insect-resistant transgenic tobacco plants expressing a serine protease inhibitor, bovine spleen trypsin inhibitor (BSTI), or a biotin-binding protein, avidin, were investigated. Both proteins could potentially affect this beetle, since avidin is known to be insecticidal to many beetle species and C. novaezelandiae midguts were shown to contain high levels of trypsin, a protease powerfully inhibited by bovine pancreatic trypsin inhibitor (a BSTI homologue) in vitro. Newly emerged field-collected adult C. novaezelandiae were fed exclusively for 280 days on Spodoptera litura larvae raised either on non-transgenic control, transgenic avidin (55 ppm) or transgenic BSTI (68 ppm) tobacco. Despite this long-term exclusive diet, there was no treatment effect on survival or fecundity and only minor and transient effects on beetles were observed. Data pooled across time and genders showed control-prey-fed beetles weighed 3% more than BSTI-prey-fed beetles and avidin-prey-fed beetles consumed 3-4% fewer prey than control- or BSTI-prey-fed individuals. Females in all treatments gained more mass and survived longer than males. Low exposure to the proteins because of dilution and deactivation within the prey is the most likely explanation for the lack of tri-trophic effects observed. Aditionally, the presence of a digestive chymotrypsin only partially inhibited by BSTI may provide an alternative path for proteolysis.

Stability of antioxidants in an apple polyphenol-milk model system.

The stability of antioxidants in an apple polyphenol-milk model system was examined. The model system consisted of skim milk fortified with pH-neutralised apple polyphenols (AP, 0-200mg per 100ml milk), with or without ascorbic acid (100mg per 100ml milk). Physical and chemical changes were evaluated after thermal treatment (120°C, 5min) and oxidative storage (20°C and 38°C, up to 12 weeks). Antioxidant capacity was determined using both oxygen radical absorbance capacity (ORAC) assay and ferric reducing antioxidant power (FRAP) assay. Significant antioxidant capacity was detected in the presence of milk. Antioxidant capacity was retained during thermal treatment but decreased slowly during storage. The concentration of ascorbic acid decreased rapidly, and was close to zero after 2-week storage at 38°C or 10-week storage at 20°C. The brownness of the polyphenol-milk system increased over storage duration of 0-12 weeks; this effect was retarded by the addition of ascorbic acid. This high polyphenol-milk has demonstrated good physical stability.

Using phytochemicals to enhance health benefits of milk: impact of polyphenols on flavor profile.

The focus of new product development of functional foods is not only on the associated health benefits but also on the sensory properties of the finished product. A trained panel (n=13) assessed 5 milk-based beverages fortified with added apple or grape seed polyphenols and a control using descriptive analysis techniques. The resulting vocabulary consisted of 16 odor, taste, flavor, and mouthfeel attributes, complete with reference standards and scale intensities. Panelists differentiated between samples using all 16 attributes in the vocabulary (P<0.001). Samples fortified with polyphenols, sourced from grape seed and apple extracts, differed significantly. Bitterness and UHT (ultra-high temperature) odor and flavor were the key drivers of product difference. Relatively small (but still significant) differences were identified between those containing polyphenols from the same plant source but different suppliers. We concluded that both grape seed and apple polyphenols suppress the flavor characteristics of the milk, with apple polyphenols having more of an impact than grape seed polyphenols. In particular, the high level of bitterness in apple extracts has large flavor profile implications for product development.