EFFECT OF ENHANCED ATMOSPHERIC CARBON DIOXIDE ON THE NUTRITIONAL QUALITY OF SELECTED DIETARY VEGETABLES

Abstract

Besides increasing global temperature, enhanced atmospheric carbon dioxide is affecting physcio-chemical and nutritional characteristics of crops and vegetables. In order to evaluate the hypothesis that climate change is threatening food quality, the effect of enhanced atmospheric CO2 on nutritional, elemental and fatty acid composition of dietary vegetables has been investigated. Dietary vegetables including tomato (Lycopersicon esculentum), chili (Capsicum annuum), onion (Allium cepa), okra (Abelmoschus esculentus), cucumber (Cucumis sativus), spinach (Spinacia oleracea), carrot (Daucus carota), pea (Pisum sativum), cauliflower (Brassica oleracea), radish (Raphanus sativus), turnip (Brassica rapa) and eggplant (Solanum melongena) were grown in ambient (400 μmol mol-1) and elevated (1000 μmol mol-1) concentration of CO2 in green houses. Edible parts of the vegetables (fruit/flower/tuber/seeds or leaves) were collected on maturity and analyzed. Enhanced CO2 has largely disturbed the nutritional balance of vegetables. A significant increase in carbohydrates and crude fiber at the cost of protein, vitamin C and fat contents was observed. Elements behaved inconsistently with a general decreasing trend. The results revealed that with a substantial increase in yield, nutritional quality of dietary vegetables unfavorably altered under CO2 enrichment with accumulated sugars and diminished proteins and vitamin C. Plants were examined for their physical characteristics and chemical composition. Previously known standard procedures were applied for chemical analysis. Samples were analyzed in triplicate and standard deviation was calculated, Student’s t test was applied on data using SPSS 16. Results were quoted as significant at (P≤0.05), non-significant (ns) at P>0.1 and trend at 0.05<P≤0.1. Nutritional balance of majority of the vegetables studied was disturbed by CO2 enriched atmosphere. Two varieties of tomato were analysed and it was observed that protein content of tomato varieties were reduced by 13.64% and 18.27% and vitamin C by 20.02% and 24.72% for mature stages and 9.59% for premature stage. Increase in sugar content with elevated CO2 was 16.12% and 20.85% for mature and 14.16% for premature tomato. Elemental composition of tomato was disturbed by enhanced CO2 with increased C, H, Ca, Fe and iv

Cu and reduced N, Mg, Zn, Mn, Pb, Ni, Cr and Cd. Most of the fatty acids including essential fatty acids i.e. linoleic acid and linolenic acid, were reduced by elevated CO2. Enhanced CO2 disturbed nutritional, elemental and fatty acid composition of capsicum varieties. Five varieties of capsicum were analysed. Observed reduction in protein was from 25.10% to 31.62% and in vitamin C it was from 11.84% to 15.66% for mature red stages and 8.98% to 12.12% for premature green stages of capsicum. Sugar contents were increased in the range 11.83% to 13.86% in red stages and 9.66% for the green stage of on variety. Elemental composition of capsicum varieties was disturbed by elevated level of CO2. Elements like C, H, Fe and Mn were increased while Ca, Mg, N, Zn and Pb were decreased. Response of capsicum fatty acids to enhanced CO2 was not same, however a general decreasing trend was observed. Enhanced CO2 altered nutritional quality of onion with reduced protein and vitamin C and increased sugars. For four varieties of onion the observed decrease in protein with elevated CO2 ranged from 12.01% to 19.53% and that of vitamin C ranged from 17.14% to 21.64%. Total sugar content was increased by 11.24%. Among the elements, C and Zn were increased while N, Mn, Fe, Pb and Cr were decreased. Different fatty acids of onion bulbs responded differently to enhanced CO2, with a general decreasing trend. Elevated CO2 reduced the nutrient composition of okra. Protein content of okra was reduced by 23.95% and 18.24% and vitamin C content was reduced by 17.72% and 13.66% for two varieties. Total sugar content of okra increased by 18.73% and 19.34%. Elemental composition of okra was disturbed by elevated CO2 with increased C, Ca and Fe and decreased N, Mg, Zn, Mn and Pb. Fatty acids of okra were mostly decreased by enhanced CO2. Enhanced CO2 decreased the protein content of cucumber by 11.15%, vitamin C by 18.57% and increased total sugars by 15.20%. Elements like C, H, Ca and Mg were increased while N, Zn, Mn and Fe were decreased by elevated CO2. Elevated CO2 mostly decreased the fatty acid content of cucumber with reduced linolenic acid, and linoleic acid. v

Atmospheric CO2 enrichment disturbed the nutritional balance of spinach with 15.88% reduction in protein and 15.72% reduction in vitamin C. Among elements, C, H and Ca were increased while N, Zn, Mn, Fe, Pb, Ni, Cu and Cr were decreased. Elevated CO2 decreased almost all of the fatty acids in spinach leaf. The decrease was more pronounced for major fatty acids as compared to minor fatty acids. Elevated CO2 affected the nutritional composition of root vegetables. Protein content of carrot, radish and turnip root tubers was decreased by 24.30%, 18.83% and 18.17% respectively by enhanced CO2. Vitamin C was reduced by 9.09% for carrot, 12.93% for radish and 21.87% for turnip. Sugar content was increased by 12.99% and 19.64% by CO2 enrichment for radish and turnip respectively. Elemental and fatty acid composition of root vegetables were also disturbed by enhanced CO2. Nutritional composition of pea was disturbed by enhanced CO2 with 13.42% reduction in protein, 13.95% reduction in vitamin C and 13.14% increase in total sugars. Elements like C, H and Mn were increased while N, Ca, Mg, K and Fe were reduced. Elevated CO2 decreased linoleic, linolenic and oleic acids in pea lipids. Elevated CO2 decreased the protein content of cauliflower by 15.55% and Vitamin C by 18.59%. Concentration of C and H were increased and that of N, S, Ca, Zn, Mn, Fe, Cu and Cr were decreased. Enhanced CO2 decreased the fatty acid content of cauliflower oil including linolenic, palmitic and linoleic acid. Protein and vitamin C content of eggplant were decreased with enhanced CO2. The decrease was 11.36% for protein and 15.96% for vitamin C. Elements like C, H and Ca were increased while N, Mg, K, Zn, Mn and Fe were decreased. Most of the fatty acids were reduced by elevated CO2. Vegetables responded differently to enhanced CO2 and more interestingly, even different varieties of the same vegetable showed different changes. Although the data is on a limited scale, the message is loud and clear - enhanced atmospheric CO2 has adversely affected the nutritional balance of dietary vegetables.