Phenolic contents, antioxidant potential and associated colour in sweet sorghum syrups compared to other commercial syrup sweeteners

Authors: Eggleston, Gillian; Boue, Stephen; Bett Garber, Karen; VERRET, CHARDCIE - Audubon Sugar Institute; Triplett, Alexa; Bechtel, Peter

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2020
Publication Date: 7/19/2020
Citation: Eggleston, G., Boue, S., Bett Garber, K., Verret, C., Triplett, A., Bechtel, P. 2020. Phenolic contents, antioxidant potential and associated colour in sweet sorghum syrups compared to other commercial syrup sweeteners. Journal of the Science of Food and Agriculture. https://doi.org/10.1002/jsfa.10673.
DOI: https://doi.org/10.1002/jsfa.10673

Interpretive Summary: Knowledge of the nutritional and dietary content of sweet sorghum syrups, compared to other common food-grade syrups, will expand sorghum utilization as a food source and facilitate its marketing. Phenolic, antioxidant activity, and related color data for commercial high fructose corn syrup (HFCS), corn, honey, maple, agave, rice, and grain sorghum syrups (three brands) were compared to ten commercial sweet sorghum syrups. Sweet sorghum syrups contained dramatically higher (P<0.05) total phenolic contents TPC (6471 ± 1823 mg/L) compared to the other syrups (596 ± 497 mg/L). Antioxidant activities of the syrups were measured as 2,2-diphenyl-1-picryl hydrazyl (DPPH) antioxidant radical scavenging activities (RSA) and oxygen radical absorbance capacity (ORAC) values. High fructose corn syrup (HFCS), corn, white grain sorghum, and rice syrups had negligible and low DPPH-RSA and ORAC values, respectively. TPC, DPPH-RSA, ORAC, and color values of the sweet sorghum syrups were dramatically (P<0.05) higher than for the other syrups and highly related. Color of the syrups was measured at pH 4.0, 7.0, and 9.0 and wavelengths of 280, 320, 420, and 580 nm. The natural color of the syrups correlated strongly to TPC, particularly when measured at pH 9.0 (sensitive to phenolic colorants) and 320 nm (sensitive to hydroxycinnamic derivatives) closely followed by 420 nm. Color of sweet sorghum syrups easily measured at pH 9.0 and 420 nm could be a useful indirect measure of total phenolics and antioxidant capacity by industry, and further studies are now warranted.

Technical Abstract: BACKGROUND: Knowledge of the bioactive content of sweet sorghum syrups compared to other common food-grade syrups will expand their utilisation as a food source. Total phenolic content (TPC), phenolics evaluated by high-performance liquid chromatography, antioxidant 2,2-diphenyl-1-picryl hydrazyl (DPPH) radical scavenging activities and oxygen radical absorbance capacity (ORAC), as well as colour of high-fructose corn syrup (HFCS), corn, honey, maple, agave, rice and grain sorghum syrups, were compared to 10 commercial sweet sorghum syrups. RESULTS: Sweet sorghum syrups contained markedly higher (P = 0.05) TPC (6471 ± 1823 mg L-1) compared to the other syrups (596 ± 497 mg L-1). HFCS, corn, white grain sorghum and rice syrups had negligible and low DPPH radical scavenging activities and ORAC values, respectively. DPPH activities, ORAC and colour values of the sweet sorghum syrups were also markedly (P = 0.05) higher than other syrups and highly related. The predominant phenolic components identified in sweet sorghum syrups were phenolic acids. Ellagic acid and protocatechuic acid were found in sorghum syrups ranging in concentration from 335–1177 and 53–485 ~g g-1, respectively. Sinapic acid was detected in several sorghum syrups, ranging in concentrations between 21 and 3654 ~g g-1. CONCLUSION: HFCS, corn, white grain sorghum and rice syrups demonstrated low bioactivity with negligible and low DPPH activities and ORAC values, respectively. The TPC, DPPH, ORAC and colour values of the sweet sorghum syrups were related to each other and markedly (P = 0.05) higher compared to the other syrups. Phenolic acids were the predominant phenolic compounds identified in sorghum syrups and represent potential for health benefits.