Impact of Huanglongbing (HLB) on grapefruit pectin yield and quality during grapefruit maturation

Authors: Ferguson, Kyle; Cameron, Randall - Randy; Dorado, Christina; Bai, Jinhe; FERRAREZI, RHUANITO - University Of Florida; DA CRUZ, MARIA - Universidade Estadual De Maringá

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/13/2020
Publication Date: 12/15/2020
Citation: Ferguson, K.L., Cameron, R.G., Dorado, C., Bai, J., Ferrarezi, R., Da Cruz, M.A. 2020. Impact of Huanglongbing (HLB) on grapefruit pectin yield and quality during grapefruit maturation. Food Hydrocolloids. https://doi.org/10.1016/j.foodhyd.2020.106553.
DOI: https://doi.org/10.1016/j.foodhyd.2020.106553

Interpretive Summary: Huanglongbing (HLB) is a plant disease responsible for citrus tree decline, increased fruit drop, and deteriorated fruit quality. Citrus pectin is a billion dollar industry which may be impacted by the HLB epidemic. We compared the physio-chemical qualities of pectin in peel from HLB affected grapefruit collected from open-air trees against healthy grapefruit grown under protective screens (CUPS) at two developmental stages to ascertain HLB impacts on pectin. qPCR detected the causal agent of HLB, which determined if the tested fruit was healthy or non-healthy, and peel color and °Brix defined the fruit’s maturity. HLB affected grapefruit exhibited 16% decreased pectin yield, and significantly (p<0.05) decreased the peel’s neutral sugars, except rhamnose. HLB affected pectin exhibited significantly (p<0.05) increased arabinose, galactose, and lower amounts of galacturonic acid (GalA) sugars, thus a lower Homogalacturan/Rhamogalacturan 1 ratio, and a lower degree of branching (DBr) compared to healthy peel pectin. HLB affected pectin had a 7% lower outside degree of methylation (DMoutside) and 28% decreased degree of blockiness (DB). The DB, absolute degree of blockiness (DBabs), degree of methylation (DM), and DMoutside of HLB affected pectin indicates a larger number of non-endopolygalacutronase digestible GalA blocks suggesting HLB affected grapefruit may exhibit a more random methylation pattern. Maturation resulted in a 20% increase in pectin yield with a 30% decrease in molecular weight and lowered the peel’s galactose and arabinose content. Understanding HLB’s and fruit maturation impact on pectin will provide customers and manufactures insight on how these factors impact the industry.

Technical Abstract: Huanglongbing (HLB) is a plant disease responsible for citrus tree decline, increased fruit drop, and deteriorated fruit quality. Citrus pectin is a billion dollar industry which may be impacted by the HLB epidemic. We compared the physio-chemical qualities of pectin in peel from HLB affected grapefruit collected from open-air trees against healthy grapefruit grown under protective screens (CUPS) at two developmental stages to ascertain HLB impacts on pectin. qPCR detected the causal agent of HLB, which determined if the tested fruit was healthy or non-healthy, and peel color and °Brix defined the fruit’s maturity. HLB affected grapefruit exhibited 16% decreased pectin yield, and significantly (p<0.05) decreased the peel’s neutral sugars, except rhamnose. HLB affected pectin exhibited significantly (p<0.05) increased arabinose, galactose, and lower amounts of galacturonic acid (GalA) sugars, thus a lower Homogalacturan/Rhamogalacturan 1 ratio, and a lower degree of branching (DBr) compared to healthy peel pectin. HLB affected pectin had a 7% lower outside degree of methylation (DMoutside) and 28% decreased degree of blockiness (DB). The DB, absolute degree of blockiness (DBabs), degree of methylation (DM), and DMoutside of HLB affected pectin indicates a larger number of non-endopolygalacutronase digestible GalA blocks suggesting HLB affected grapefruit may exhibit a more random methylation pattern. Maturation resulted in a 20% increase in pectin yield with a 30% decrease in molecular weight and lowered the peel’s galactose and arabinose content. Understanding HLB’s and fruit maturation impact on pectin will provide customers and manufactures insight on how these factors impact the industry.