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Agriculture and Agricultural Science Procedia 7 ( 2015 ) 260 – 264

Farm Machinery and Processes Management in Sustainable Agriculture, 7th International Scientific Symposium Kernel carbohydrates concentration in sugary-1, sugary enhanced and shrunken kernels Mariusz Szymaneka*, Wojciech Tanaśa, Flaieh Hammed Kassarb

a University of Life Sciences in Lublin, Department of Agricultural Machinery, Głęboka 28, 20-612 Lublin, Poland b University of AL- Muthanna, Rumaitha Samawa, Iraq

Abstract

Sweet corn remains at its optimum harvest maturity for a very short period, and quality changes rapidly following its peak. This study investigates the changes in carbohydrate concentration of three genotypes of sweet corn: sugary (su-1), sugar enhanced (se) and supersweet or shrunken (sh2) at three stages of maturity. The analysis of variance revealed differences between genotypes for carbohydrates (sugars and ) and between stages of maturity (moisture content). Average sugar concentration of su-1 corn was 5% higher than that of se corn and 52% higher than that of sh2 corn. The average starch concentration of su-1 corn was 27% lower than that of se corn and 66% lower than that of sh2 corn. The average moisture content of su-1 corn was 3% lower than that of se corn and 1% lower than that of sh2 corn.

©© 20152015 TheThe Authors.Authors. PublishedPublished by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (Peerhttp://creativecommons.org/licenses/by-nc-nd/4.0/-review under responsibility of the Centre wallon). de Recherches agronomiques (CRA-W). Peer-review under responsibility of the Centre wallon de Recherches agronomiques (CRA-W) Keywords: genotype;, maturit;, moisture; sugars; starch.

1. Introduction

In Europe, as well as in Poland, the areas cultivated with sweet corn (Zea mays L. var saccharata) have increased considerably, during the last ten years. Sweet corn eaten in the immature stage is widely used for human consumption throughout the world. It is important source of fiber, minerals, and certain vitamins. It is produced for

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2210-7843 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Centre wallon de Recherches agronomiques (CRA-W) doi: 10.1016/j.aaspro.2015.12.044 Mariusz Szymanek et al. / Agriculture and Agricultural Science Procedia 7 ( 2015 ) 260 – 264 261 three distinct markets: fresh, canning, and freezing. The sweet corn varieties suitable for processing vary according to the products, canned or frozen. In recent years, sweet corn harvested for processing has been greatly improved by selective breeding and hybridizing. Nearly all commercially grown sweet corn is now of hybrid varieties. These varieties offer greatly increased yields and better uniformity, with excellent flavor, color, and processing quality (Kumar et. al, 2006). The primary components of fresh sweet corn eating quality associated with consumer performance are flavor (mainly sweetness), kernel texture and aroma (Azanza et al., 1996). Kernel sugar concentrations have been correlated with sweetness and taste panel preference (Evensen and Boyer, 1986; Azanza et al., 1994). Sweetness and tenderness were found to be the most important in overall quality, in a study conducted with fresh and processed sweet corn. Kernel sucrose concentration is regulated by carbohydrate metabolism during kernel development. New varieties of sweet corn have been developed with improved consistency, taste and shelf life (Kamol and Pulam, 2007). In sweet corns, the enhancement of sweet components in kernels is made successfully by reduction of starch synthesis activities and increase in sucrose accumulation. There are many different endosperm mutations in corn that influence kernel carbohydrate metabolism (Coe and Polacco 1994). Traditional sweet corn is homozygous for the sugary 1 (sh1) mutation. Comparison to normal , su1 accumulate more sugar and a highly branched, water soluble form of starch known as phytoglycogen at harvest maturity. Sweet corn su1 varieties are characterized by a rapid loss of kernel quality after harvest due to the conversion of sugars to starch and moisture loss (Azanza et al., 1996). This rapid decline in quality restricts the time available for shipment from growing regions to major marketing areas and provides a narrow window to the sweet corn processing industry (Marshall and Tracy, 2003). Shrunken2 (sh2) and sugary enhancer1 (se1) are endosperm mutations of increasing importance to the sweet corn industry due to their superior eating quality. Preferred by consumers, owing to greater (two to three times more) kernel sucrose concentration (sh2) at fresh harvest retain higher sugar and moisture concentration for longer postharvest periods than the traditional variety (sh1). These varieties retain higher sugar and moisture concentration for longer postharvest periods and have only trace levels of phytoglycogen in comparison to su1 kernels (Malvar et al, 1997). This longer postharvest life provides the industry with more time to transport, process, and market a product with superior eating quality (Azanza, 1996). Sweet corn genotypes with either sh2 or su1 se1 have also been shown to be preferred by consumers in taste panels (Evensen and Boyer, 1986). Supersweet varieties have become the dominant type produced in virtually all the major sweet corn producing regions of the Poland. Despite the desirable attributes of sh2 and su1 se1 corn, the utilization of these two endosperm mutations has been hindered by reduced field emergence, seedling vigor and stand uniformity and stand uniformity (Douglass, 1993). Goldman and Tracy (Goldman and Tracy, 1994) reported that kernels containing the sh2 mutant have a much smaller endosperm than su1 due the effects of this mutant on starch synthesis. Reductions in endosperm size result in smaller, lighter kernels. Several kernel characteristics in fresh sweet corn have been related to sensory quality. Pericarp thickness has been negatively associated with the sensory perception of tenderness (Juvik and Labonte, 1988). Sweet corn flavor and texture are associated with the chemical composition of the kernel, the structural compactness of starch granules, and the cellular structure of the endosperm (Tracy, 2001). The objective of the study was to measure carbohydrates concentrations of three genotypes of sweet corn: sugary (su-1), sugar enhanced (se) and supersweet or shrunken (sh2) at three stages of maturity (SM).

2. Materials and methods

Three genotypes of commercial sweet corn cultivars, a cultivar recessive for the sugary (su-1) (Boston), sugar enhanced (se) (Anawa) and supersweet or shrunken (sh2) (Candle) were compared during maturation period for carbohydrate composition and yield for processing quality. Sweet corn for these studies was grown during 2013 in University of Life Sciences Research Station, near Lublin, Poland. The cultivars were grown in isolation, about 200 m, from one another to reduce the likelihood on cross-pollination. Harvests of ears for physical and chemical analyses were made at 4 – day intervals from 20 to 32 days after pollination (DAP). These stages were chosen because sugars reach maximum levels at about 21 DAP and sweet corn typically is harvested at this stage of maturity (Carey et al., 1984). At each harvest date, ears were hand picked at random for each genotype. Directly after harvest, ears were husked and silk was removed. Next the ears were frozen in liquid nitrogen to stop all metabolic activity. Thirty kernels of corn ears were randomly removed and ground into powder in laboratory grinder, and stored in freezer at about -20qC for subsequent carbohydrate analyses. 262 Mariusz Szymanek et al. / Agriculture and Agricultural Science Procedia 7 ( 2015 ) 260 – 264

Measurement of sugar contents was made using the DNS method following acid hydrolysis (PN-EN ISO 10520, 2002). The reducing sugars were determined prior to the hydrolysis by means of the DNS method. The starch content was determined through the difference between the total content of sugars and the content of sugars soluble in ethyl alcohol (40% vol/vol). The sucrose content was established through the difference between the content of sugars soluble in ethyl alcohol and the content of reducing sugars. To determine the reducing sugar content with the DNS method, a test tube was filled with 0.5 cm3 of the tested solution and 1.5 cm3 of 3-5- dinitrosalicylic acid (DNS) and then boiled for 5 minutes in a bath of boiling water. After cooling down, 6 cm3 of distilled water was added to make a total volume of 8 cm3. Next, the sample extinction was read against a reagent assay at a wavelength of O = 550 nm. The extinction measurement results were referenced to the model curve. The sugar content was determined in relation to the kernel dry mass. The experiments were replicated thrice in 100-gram samples for each variety and the average values were reported. The moisture content of the kernels was determined using the ASAE (1983) method. This involved oven drying of samples at 103°C for 72 h. The samples were allowed to cool in a desiccator after which the weights were recorded. Three samples were used and the average moisture content was reported. Data were subjected to analysis of variance (ANOVA). Comparison of means was conducted with Tukey's least significant difference (LSD) test, at a significance level p = 0.05. All statistical analysis was performed using the Statistica 6.0.

3. Results and discussion

Sweet corn kernel concentration of carbohydrates and moisture are presented in Table 1.

Table 1. Mean sweet corn kernel concentration of carbohydrates and moisture of three fresh sweet corns at three stages of maturity.

Stage Carbohydrates Genotypes Varieties of Sugar, % Starch, % Moisture, % maturity Sugar, % Starch% I 5.2a 15.7a 74.6a Boston II 5.3b 20.1ba 69.4ba III 4.6cab 24.6cab 64.2cab I 5.9a 16.1a 72.5a Bonus II 5.7b 19.2ba 67.1ba su-1 III 4.9cab 23.8cab 60.2cab I 5.4a 15.2a 74.6a Jubilee II 5.1b 19.6ba 66.8ba III 4.6cab 23.7cab 58.7cab Mean - 5.1 19.7 67.5 LSD (0.05) - 0.4 3.2 5.1 I 6.5a 12.3a 72.3a Anava II 5.2ba 16.3ba 61.2ba III 4.7ca 18.8ca 59.4ca I 6.2a 11.9a 71.9a Champ II 4.8ba 14.2ba 65.5ba se III 4.3ca 17.2cab 57.8cab I 6.8a 12.8a 74.6a Dallas II 5.6ba 15.6ba 65.7ba III 5.1ca 19.9cab 59.7cab Mean - 5.4 14.4 65.3 LSD (0.05) - 1.1 2.1 4.3 I 8.3a 6.3a 71.9a Candle II 7.6ba 6.8b 67.1ba III 7.2cab 7.6c 59.6cab I 8.9a 6.1a 73.6a sh2 Challenger II 7.6ba 6.7b 67.3ba III 6.9cab 7.5c 58.6cab I 8.7a 5.8a 75.2a Sheba II 8.2ba 6.6b 67.2ba Mariusz Szymanek et al. / Agriculture and Agricultural Science Procedia 7 ( 2015 ) 260 – 264 263

Stage Carbohydrates Genotypes Varieties of Moisture, % III 7.6cab 7.3c 61.6cab Mean - 7.8 6.7 66.9 LSD (0.05) - 0.4 1.6 4.6 Genotypes 0.6 5.4 66.9 LSD (0.05) Within each column, the same letter indicates the significant difference at p < 0.05.

The analysis of variance showed significant difference between genotypes type, and stage of maturity for carbohydrates and moisture concentration. Carbohydrates per kernel did not differ between cultivars. The delay of the harvest date affected the changes of moisture, sugars and starch concentrations. A similar trend was reported by Simonne et al. (1999), Suk and Sang (1999), Waligóra (2002), Warzecha (2003) and Liu-Peng et al. (2003). The results show that delaying the harvest date decreasing moisture and sugars and leads to an increase in the starch concentrations. Negative associations between sugar content and starch content were also observed by Dudley and Lambert (1992), Ha (1999), Kumari et al. (2006). The highest decrease of moisture contents (21.3%) was obtained for the Jubilee variety and the lowest (13.9%) for the Boston variety. The average moisture content of the su-1 sweet corn varieties (17.3%) was 19.6% lower than the moisture content of the se varieties (13.9%) and 21.3% lower than sh2 varieties (21.3%). The average sugars concentrations of the three cultivars of su-1 genotype types (5.6%) for I stage of maturity was 16% lower than the sugars concentration of III stage of maturity (4.4%). Respectively for cultivars of se and2 sh genotype types this was obtained: 27.6% and 15.8%. Results from the investigation demonstrate that sugars concentration in sh2 kernels is significantly higher by about 32% in I date of harvest, by about 50% in II date of harvest and by about 53% in III date of harvest than sugars concentration in se kernels and by about 48% in I date of harvest, by about 47% in II date of harvest and by about 53% in III date of harvest than sugars concentration in su-1 kernels. Table 1 indicates starch concentration was 56.0% higher in su-1 in III stage of maturity than in I stage of maturity. The starch concentrations of se and2 sh genotype types were 51.5% and 19.6% higher, respectively. Starch concentration in sh2 kernels is significantly lower by about 105% in I date of harvest, by about 143% in II date of harvest and by about 151% in III date of harvest than sugars concentration in se kernels and by about 160% in I date of harvest, by about 192% in II date of harvest and by about 224% in III date of harvest than sugars concentration in su-1 kernels.

4. Conclusion

The results of this study indicate clearly that the date of sweet corn harvest is the most important factor in maintaining fresh sweet corn quality. It was observed that the more mature sweetcorn (III date of harvest) had larger kernels and the kernels were more compact on the cob, while the less mature (I date of harvest) kernels were smaller and there were still some spaces between the kernel rows. The delay of the corncobs harvest date affected the sweet corn quality. The moisture content and sugars concentration decreased but starch level increased. The rise of starch concentration was more quickly between su-1 sweet corn varieties than se 2or sh .

References

ASAE Standards, 1983. S352.1. Moisture measurement – and . St. Joseph Mich.: ASAE. Azanza, F., Klein, B.P., Juvik, J.A., 1996. Sensory characterization of sweet corn lines differing in physical and chemical composition. Journal of Science 61, 253-257. Azanza, F., Juvik, J.A., Klein, B.P., 1994. Relationship between sensory quality attributes and kernel chemical compositions of fresh and frozen sweet corn. Journal of Food Science 61(1), 253-257. Carey, E.E., Rhodes, A.M., Dickinson, D.B., 1982. Postharvest levels of sugars and sorbitol in sugary enhancer (su se) and sugary (su Se). HortScience 17, 241–242. Coe, E.H., Polaco., 1994. Gene list and working maps. Maize Genet. Coop. Newslett., 68, 157-208. Douglass, S.K., Splittstoesser, W.E., 1993. Sweet corn seedling emergence and variation in kernel carbohydrate reserves. Seed science and technology 21(2), 433-445. Dudley J.W., Lambert, R.J., 1992. Ninety generations of selection for oil and protein in maize. Maydica 37, 1-7. 264 Mariusz Szymanek et al. / Agriculture and Agricultural Science Procedia 7 ( 2015 ) 260 – 264

Evensen, K.B., Boyer, C.D., 1986. Carbohydrate composition and sensory quality of fresh and stored sweet corn. Journal of the American Society for Horticultural Science 111(5), 734-738. Goldman, I.L., Tracy, W.F., 1994. Kernel protein concentration in sugary-1 and shrunken-2 sweet corn. HortScience 29(3), 209-210. Ha, V., 1999. Genetic analysis of some yield components and kernel quality in sweet corn. Romania Agrıculture Research 11-12, 9-20. Juvik, J.A., Labonte, D.R., 1988. Single-kernel analysis for the presence of the enhancer (se) gene in sweet corn. HortScience 23, 384-386. Kamol, L., Pulam, T., 2007. Breeding for increased sweetness in sweet corn. International Journal of Plant Breeding 1(1), 27-30. Kumari, J., Gadag, R.N., Jha, G.K., 2006. Heritability and correlation studies in sweet corn for quality traits, field emergence and yield. MNL 80,18-19. Marshall, S.W., Tracy, W.F., 2003. Sweet corn. In: Ramstad P.E., White P. (eds): Corn Chemistry and Technology. American Malvar, R.A., Revilla, P., Cartea, W.F., Ordas. 1997. A Field corn inbreds to improve sweet corn hybrids for early vigor and adaptation to European conditions. Maydica 42(3), 247-255. Liu-Peng, Hu-Chang Hao, Dong-Shu Ting, Wang-Kong Jun., 2003. The comparison of sugar components in the developing grains of sweet corn and normal corn. Agricultural Science in China 2, 258-264. PN-EN ISO. 2002. ISO 10520: Native starch - Determination of starch content - Ewers polarimetric method. Poland: ISO (in Polish). Simonne, E., Simonne, A., Boozer, R., 1999. Yield, ear characteristics, and consumer acceptance of selected white sweet corn varieties in the southeastern United States. Hort Technology 1, 289-293. Suk, S.L., Sang, H.Y., 1999. Sugars, soluble solids and flavor of sweet, super sweet and waxy corns during grain filling. Korean Journal of Crop Science 44, 267-272. Tracy, W.F., 2001. Sweet corn, p. 155–197. In: A.R. Hallauer (ed.). Specialty corns. 2nd ed. CRC Press, Boca Raton, Fla. Waligóra, H., 2002. Kukurydza cukrowa i możliwości jej uprawy w Polsce. Wieś Jutra 47, 20-23. Warzecha, R., 2003. Słodki smak kukurydzy. Owoce Warzywa Kwiaty 6, 20-21.