Galen Peiser

Phenylalanine ammonia lyase inhibitors control browning of cut lettuce

Inhibitors of the first enzyme in the phenylpropanoid pathway, phenylalanine ammonia lyase (PAL), were used to investigate the role of phenolic metabolism in browning of lettuce tissue. Excised 4 7-cm midrib segments were soaked fo r1ha t20°C in aqueous solutions of the PAL inhibitors, a-aminooxyacetic acid (AOA; 0.1‐10 mM), 2-aminoindan-2-phosphonic acid (AIP; 50‐100 mM), and a-aminooxi-b-phenylpropionic acid (AOPP; 200 mM). Browning of the cut ends and uncut surfaces was measured using a visual score, and CIE color values (L*, a*, b*). Overall browning potential was measured as the absorbance at 340 nm of an aqueous extract of the tissue. The visual scores were more highly correlated with hue angle than with the a* and b* values; there was no correlation with the L* values. Ethylene applied at 5 m ll 1 had no effect upon browning compared with the air treatments. AIP at 50 mM and AOPP at 200 mM effectively inhibited browning; AOA was less effective requiring 3‐10 mM to reduce browning. These results confirm the view that for browning to occur in lettuce PAL activity is required to form phenolics that are subsequently oxidized and polymerized.

Use of controlled atmospheres and heat treatment to maintain quality of intact and minimally processed green onions

To maintain high quality and to extend the shelf life of intact and minimally processed (removal of roots and compressed stem) green onions (Allium cepaA. fistulosum), the potential benefits of controlled atmospheres (CA) and heat treatment were evaluated. Atmospheres of 0.1‐0.2% O2 or 0.1‐0.2% O2 containing 7.5‐9% CO2 were the CA conditions that best maintained the visual appearance and prolonged shelf life to more than 2 weeks at 5°C in both intact and cut onions. No CA treatment completely controlled extension, growth or ‘telescoping’ of the inner white leaf bases of the minimally processed onions at 5°C. Heat treatment (55°C water for 2 min) of the white leaf bases effectively controlled ‘telescoping’ of cut onions stored at 5°C. Total soluble sugars generally decreased in intact and minimally processed green onions, but were maintained in heat-treated cut onions. Heat treatment did not affect thiosulfinate concentrations during 14 days at 5°C, except for treated cut onions not stored under CA.

Chlorophyll destruction in the presence of bisulfite and linoleic acid hydroperoxide

Abstract Chlorophyll was rapidly destroyed in the presence of bisulfite and linoleic acid hydroperoxide. Both bisulfite and linoleic acid hydroperoxide were required for chlorophyll destruction and both were consumed in the reaction; however, there was no oxygen requirement. Chlorophyll destruction occurred most readily in the slightly acidic pH region with little destruction occurring above pH 8. The free radical scavengers, hydroquinone and α-tocopherol, were very effective at inhibiting chlorophyll destruction, but the singlet oxygen quenchers, β-carotene, 2,5-dimethylfuran and 1,3-diphenylisobenzofuran, were only slightly effective. The addition of metal chelators indicated that metals were not participating in the reaction. The evidence indicates that chlorophyll was destroyed by a free radical mechanism. Based on the present results and that of others, it is suggested that chlorophyll was destroyed via oxidation by the alkoxy radical which was produced during the decomposition of linoleic acid hydroperoxide by bisulfite.

Acetaldehyde Is a Causal Agent Responsible for Ethanol-Induced Ripening Inhibition in Tomato Fruit

Inhibition of tomato (Lycopersicon esculentum Mill.) fruit ripening by exogenously applied ethanol was shown to be caused by elevated endogenous levels of acetaldehyde (AA). Exposure of excised pericarp discs of mature-green tomato fruit to ethanol or AA vapors produced elevated levels of both compounds in the tissue, but only the levels of AA were associated with ripening inhibition. Ripening inhibition was dependent on both the applied concentration and the duration of exposure. Discs treated with inhibitory levels of AA had levels of ethanol that were elevated but below that associated with inhibition of ripening. The in vivo activity of alcohol dehydrogenase was inhibited 40 to 60% by 4-methylpyrazole (4-MP), a competitive inhibitor of this enzyme. The inhibitory effect of ethanol on ripening was reduced by the simultaneous application of 4-MP. Tissue treated with 4-MP plus AA vapors had higher endogenous levels of AA and ripening was inhibited longer than in tissue without 4-MP. The tissue AA level resulting from ethanol or AA application appears to be the critical determinant of ripening inhibition.

Phytotoxic sesquiterpenoids from Canella winterana

Abstract Nine new drimane-type sesquiterpenoids: 3α-acetoxypolygodial, 3α-acetoxypolygodial 12-dimethyl acetal, 9-deoxymuzigadial 12α-acetal, 9-deoxymuzigadial 12β-acetal, 3β-acetoxypolygodial 12α-acetal, 3β-acetoxypolygodial 12β-acetal, 9-epideoxymuzigadial, 3β-acetoxypolygonal and muzigaal, were isolated from the leaves of Canella winterana , together with six previously known sesquiterpenoids; muzigadial, 3β-acetoxypolygodial, 3β-acetoxycinnamolide, isopolygodial, polygodial 12α-acetal and drimenol. Unambiguous assignments of all 1 H and 13 C signals of 15 sesquiterpenoids were established by 2D NMR experiments.