Pectin is a anionic polysaccharide polymer,which is widely used in food industry as emulsifier,gel agent,thickener,etc.,with good market application value.Commercially,pectin is mainly extracted from citrus and apple peels,citrus pectin has high molecular weight and stable property,therefore,it is often used as a raw material for extraction.In this paper,addressed the problems of complex residues,high viscosity,and enhanced application performance of pectin in extraction residue of whole peel in the citrus pectin industry.Citrus pectin raw materials were classified for extraction to explore the effects of powder size,cortical location,extraction conditions,and acids types on the pectin extraction.Preparation of pectin-amino acid complex by amino acid modified citrus low methoxyl pectin,studied the effects of amino acids types,pectin mass fraction,mass ratio of pectin and amino acid,etc,.on the gel strength of pectin-amino acid complex,the FT-IR spectrum,thermal mechanical properties,rheological properties of pectin-amino acid complex were also analyzed.Dry heat reaction of citrus low methoxyl pectin(LMP)with soy peptide(SP),corn peptide(CP),and whey protein peptide(WPP),the complexes were emulsified with camellia seed oil,the effects of peptide type,mass ratio of pectin and peptide,and dry reaction time on the particle size,microstructure,and stability of the emulsion were investigated.Subsequently,the in vitro digestion properties andβ-carotene bioaccessibility ofβ-carotene loaded emulsions were examined.The study reached the following conclusions:(1)Classified extraction of pomelo peel pectin from citrus products,the results showed that particle size distribution of different cortical powder was different,it is possible to achieve wind grading after full peel crushed.Furtherly,extracted pectin from different parts of the skin,found that when the optimum powder size was 60mesh,for outer layer the best extracted was heated air-dried with citric acid,the yield was 12.45%,the middle layer the best extracted was heated air-dried with hydrochloric acid,with a yield of 16.87%,the inner layer was best dried by infrared-dried with hydrochloric acid,the yield was 18.02%.The results showed that the inner layer had the highest extraction rate,second was the middle layer,and the outer layer had the lowest extraction rate,the yield of pectin extracted by stratified layer was higher than that of whole peel.The galacturonic acid of pectin extracted from pomelo peel reached 78%,and the degree of esterification reached more than68%,indicated that the extracted pectin was high methoxyl pectin,which was further confirmed by infrared spectrum analysis.(2)The effects of amino acid modification on the gel properties of citrus low methoxyl pectin showed that when add different kinds of amino acids(lysine,glycine,and glutamic acid)to low methoxyl pectin solution with a mass fraction of 1.5%prepared with p H 4.0 phosphate buffer solution,in which the mass ratio of pectin to amino acid was 5:1,and then add Ca2+solution with a mass fraction of 0.5%,pectin-amino acid complex formed maximum gel strength,the pectin-lysine complex showed the maximum strength,102 g,which was 2 times higher than that of the control group.Modification of amino acids is beneficial to obtain low methoxyl pectin gel with high strength and stable structure under the low Ca2+mass fraction.Intermolecular interaction studies suggested that amide bond or electrostatic force is the main interaction force between pectin and amino acids to maintain the stability of pectin-amino acid complexes.(3)The pectin-peptide complexes were confirmed by FT-IR spectroscopy,emulsion particle size measurement showed that with the increased of dry heating time and the amount of peptide added,the stability of the pectin-peptide complex emulsion increased firstly and then decreased.The best conditions were dry heating for 12h at pectin:peptide mass ratio was 4:1,for the three pectin-peptide emulsions,the best were LMP-SP and LMP-WPP.In vitro digestion ofβ-carotene loaded emulsions showed that pectin-peptide complexes stabilized emulsions could pass through the oral,gastric,gradually released in the small intestine,helped to increase the bioavailability of active substances such asβ-carotene. |