Tailoring microstructure and mechanical properties of pectin cryogels by modulate intensity of ionic interconnection.

Porous morphology and mechanical properties determine the applications of cryogels. To understand the influence of the ionic network on the microstructure and mechanical properties of pectin cryogels, we prepared low-methoxyl pectin (LMP) cryogels with different Ca2+ concentrations (measured as R-value, ranging from 0 to 2) through freeze-drying (FD). Results showed that the R-values appeared to be crucial parameters that impact the pore morphology and mechanical characteristics of cryogels. It is achieved by altering the network stability and water state properties of the cryogel precursor. Cryogel precursors with a saturated R-value (R = 1) produced a low pore diameter (0.12 mm) microstructure, obtaining the highest crispness (15.00 ± 1.85) and hardness (maximum positive force and area measuring 2.36 ± 0.31 N and 12.30 ± 1.57 N·s respectively). Hardness showed a negative correlation with Ca2+ concentration when R ≤ 1 (-0.89), and a similar correlation with the porosity of the gel network when R ≥ 1 (-0.80). Given the impacts of crosslinking on the pore structure, it is confirmed that the pore diameter can be designed between 56.24 and 153.58 µm by controlling R-value in the range of 0-2.

New insight into pectic fractions of cell wall: Impact of extraction on pectin structure and in vitro gut fermentation.

Pectic polysaccharides modulate gut fermentation ability, which is determined by structural characteristics. In this work, apple pectins were extracted by HCl (HAEP), NaOH (AEP), cellulase (EAEP), and in parallel cell wall pectic fractions were sequentially extracted by water (WEP), chelator (CEP) and NaOH (NEP). The aim is to comprehensively compare the impact of extraction on pectin structure and gut fermentation behavior. Results showed that high content of galacturonic acid (90.65 mol%) and large molecular weight (675 kg/mol) were detected in the HAEP. Molecular morphology of the HAEP presented high linearity, while AEP, EAEP and WEP exhibited compact filamentous structures with highly branched patterns. The AEP was characterized by high yield (33.1 g/100 g d.b.), moderate molecular weight (304 kg/mol) and large extent of rhamnogalacturonan-I region (24.88 %) with low degree of branching (1.77). After in vitro simulated gut fermentation for 24 h, total content of short-chain fatty acid (SCFA) generated with the AEP supplement increased to 36.8 mmol/L, followed by EAEP, HAEP and WEP (25.2, 24.2 and 20.3 mmol/L, respectively). Meanwhile, WEP simultaneously produced the highest ammonia content (22.4 mmol/L). This investigation suggests that the fermentation of AEP produces more beneficial SCFA and less ammonia, thus indicating a better gut fermentation property.

Study on the ice crystals growth under pectin gels with different crosslinking strengths by modulating the degree of amidation in HG domain.

The ice crystal morphology formed under a series of amidated pectin gels with various crosslink strengths were investigated. The results showed that as the degree of amidation (DA) increased, pectin chains exhibited shorter homogalacturonan (HG) regions. Highly amidated pectin exhibited a faster gelation rate and a stronger gel micro-network via hydrogen bonds. Based on cryogenic scanning electron microscopy (cryo-SEM), smaller ice crystals were formed in frozen gel with low DA, suggesting that a weaker cross-linked gel micro-network was more effective at inhibiting crystallization. After sublimation, lyophilized gel scaffolds with high crosslink strength displayed less number of pores, high porosity, lower specific surface area, and greater mechanical strength. This study is expected to confirm that the microstructure and mechanical properties of freeze-dried pectin porous materials could be regulated by changing the crosslink strength of pectin chains, which is achieved by increasing the degree of amidation in the HG domains.

A wide diversity exists in pectin structure from thirteen apple cultivars.

To emphasize that differences in pectin structure among cultivars play a crucial role in the texture and quality of fruits and vegetables, the sugar content and methyl-esterification of pectin fractions from 13 apple cultivars was studied. Cell wall polysaccharides were isolated as alcohol-insoluble solids (AIS) and subsequently extracted to yield water-soluble solids (WSS) and chelating-soluble solids (ChSS). All fractions contained significant amounts of galacturonic acid, while sugar compositions varied between cultivars. AIS and WSS pectins showed a degree of methyl-esterification (DM) > 50 %, while ChSS pectins had either a medium (∼50 %) or low (<30 %) DM. Homogalacturonan as major structure was studied using enzymatic fingerprinting. Methyl-ester distribution of pectin was described by degrees of blockiness and -hydrolysis. Novel descriptive parameters were obtained by measuring the levels of methyl-esterified oligomers released by endo-PG (DBPGme) and PL (DBPLme). Pectin fractions differed in relative amounts of non-, moderately-, and highly methyl-esterified segments. WSS pectins were mostly lacking non-esterified GalA sequences, while ChSS pectins had medium DM and many non-methyl-esterified blocks or a low DM with many intermediate methyl-esterified GalA blocks. These findings will be of help to better understand physicochemical properties of apple and its products.

The role of fructose at a range of concentration on the texture and microstructure of freeze-dried pectin-cellulose matrix cryogel.

Freeze-dried (FD) fruit and vegetable materials with a large amount of sugar are unstable. With the aim to understand the structure formation of FD products, the effects of fructose content on the texture and microstructure of FD matrix were investigated by using pectin-cellulose cryogel model. Cryogels containing fructose of 0-40% were produced using freeze-drying at three different primary drying temperatures of -40, -20, and 20°C. The resultant cryogels were characterized by texture profile analyzer, scanning electron microscope, and µCT. Results indicated that at drying temperature of -40°C, increasing fructose concentration promoted the hardness of the cryogels, and cryogels of 16% fructose obtained maximum hardness. Excessive fructose (≥20%) weakened the described hardness, while exhibiting stronger springiness and resilience. The microstructure showed that dense pores and increased wall thickness due to fructose aggregation were critical factors responsible for increased hardness. The porous structure as well as relatively large pore size were necessary for crispness, in addition, rigid pore wall with certain strength were also required. At the drying temperature of 20°C, large hetero-cavities dominated the microstructure of cryogels with 30% and 40% fructose, caused by melting inside during FD process. In this situation, lower Tm (-15.48 and -20.37°C) were responsible for cryogels' melting In conclusion, if possible, regulating fructose content and state may enable the precision texture design of FD fruit and vegetable foods.

Understanding the impact of pectin physicochemical variation on browning of simulated Maillard reaction system in thermal and storage processing.

Maillard reaction browning is one of the quality deterioration in dried fruit products, but how pectin affects Maillard reaction in the fruit drying and storage process is not clear. This study aimed at investigating the mechanism of pectin variation impact on the browning of Maillard reaction by using simulated system (l-lysine, d-fructose and pectin) in thermal (60 °C and 90 °C for 8 h) and storage (37 °C for 14 days) process. Results showed that apple pectin (AP) and sugar beet pectin (SP) significantly enhanced the browning index (BI) of the Maillard reaction system by 0.01 to 134.51 in the thermal and storage processes, respectively, which were methylation degree of pectin-dependent. The pectin depolymerization product participated Maillard reaction by reacting with l-lysine, and increasing the 5-hydroxymethyl furfural (5-HMF) content (1.25-11.41-fold) and Abs420nm (0.01-0.09). It also produced a new product (m/z 225.1245), which finally increased browning level of the system.

Influence of starch with different degrees and order of gelatinization on the microstructural and mechanical properties of pectin cryogels: A potential pore morphology regulator.

The applications of cryogels are defined by their porous morphology as well as mechanical properties. To achieve efficient regulation of porous properties for pectin cryogels, we selected starch as a potential polysaccharide regulator. Pectin/starch composite cryogels with different degrees of gelatinization were formulated, and two ways of starch gelatinization were considered: starch gelatinization occurred before or after pectin crosslinking during forming the hydrogel network. The results showed that high gelatinized starch (73.8 %-100.0 %) rendered pectin cryogels with denser pore morphology and higher mechanical strength. The pore diameter transferred from 160-200 µm to 40-60 µm with the degree of gelatinization, while the total porosity decreased by about 15 % and the specific surface area increased by about 100 m2/g. When starch gelatinization occurred before pectin crosslinking, the hydrogen bond interactions between gelatinized starch and pectin were formed to accelerate the gelation rate of the pectin Ca2+-dependent network. When gelatinization occurred after pectin crosslinking, the pre-formed pectin network delayed the breakdown of the starch crystalline structure during gelatinization. The qualitative regulation of the pore morphology in pectin cryogels by incorporating starches with varying degrees of gelatinization was confirmed.

Modulation of ice crystal formation behavior in pectin cryogel by xyloglucan: Effect on microstructural and mechanical properties.

To fully understand the role of xyloglucan (XyG) on the microstructural and mechanical properties of pectin cryogels, we formulated two types of low methoxyl pectin cryogels containing different XyG content (with or without an ionic network) using freeze-drying. The interaction between the pectin and XyG was explored, and the morphologies of ice crystals were characterized by the pore morphometric of freeze-dried scaffolds. Results showed that XyG and pectin could be cross-linked via hydrogen bonding interactions. When the ionic network was present, XyG accelerated pectin gelation but decreased the size of ice crystals during freezing, reducing the pore diameters of cryogels from 340 to 350 µm to 210-230 µm while shifting the structural thickness from 50 to 70 µm to 30-50 µm. When the ionic network was absent, the addition of XyG increased the pore size of the pectin cryogel from 30 to 50 µm to 70-90 µm, while rising the pore wall thickness from 50 to 70 µm to 70-90 µm. The ionic cross-links between the pectin chains gave freeze-dried scaffolds mechanical strength and crispiness, and the incorporation of XyG further strengthened the mechanical resistance of cryogels.

Effect of high pressure homogenization on water-soluble pectin characteristics and bioaccessibility of carotenoids in mixed juice.

The effect of high pressure homogenization (HPH) compared with simple blending and milling on mixed juice properties, including water-soluble pectin (WSP) characteristics and total carotenoid bioaccessibility (TCB) was investigated. Overall, HPH treatments, which comprised of varied pressures, passes and inlet temperature (IT) affected WSP characteristics. Increased pressure showed decreased molecular weight (Mw), galacturonic acid (GalA) content and branching, and enhanced degree of methylesterification (DM) and chain linearity, suggesting degradation of RG-I fragments. Two passes at 140 MPa enhanced GalA content, nevertheless it reduced DM, implying rearrangement of depolymerized fractions. Besides, elevated IT combined with high pressure increased GalA content and DM signifying thermo-solubilization of certain HG-rich pectin. Notably, the TCB was enhanced by higher pressure and elevated temperature, which had positive relationship with DM and chain linearity of WSP and negative correlations with GalA content and Mw. Results highlighted the potential of HPH to improve WSP characteristics to enhance TCB.

Pectin and homogalacturonan with small molecular mass modulate microbial community and generate high SCFAs via in vitro gut fermentation.

The intestinal fermentability of pectic polysaccharides is largely determined by its molecular size. In this study, fermentation properties of enzymatic-modified apple pectin (AP) and homogalacturonans (HG) with high, medium and low molecular weight (Mw) were evaluated by in vitro fermentation model, and their structural changes were also investigated. Results showed that Mw, monosaccharide contents and molecular linearity of the AP hydrolysates were reduced after microbial degradation. On the other hand, culture media supplemented with low-Mw AP (60,300 g/mol) and low-Mw HG (861 g/mol) exhibited lower pH (5.1 and 5.7, respectively) and produced higher total short-chain fatty acid contents (SCFA, 230.40 mmol/L and 187.19 mmol/L, respectively). However, reduced trends in abundance of the pectinolytic microorganisms Faecalibacterium and Eubacterium were showed as Mw of the HG decreased, whereas growth of the SCFA-producer genera Bifidobaacterium, Megasphaera and Allisonella were improved. This work confirmed that low-Mw pectin and homogalacturonan generated more beneficial metabolites, developing structure-microbiota-gut health relationship.

Salicylic acid treatment mitigates chilling injury in peach fruit by regulation of sucrose metabolism and soluble sugar content.

Peach fruit stored in the cold are susceptible to chilling injury. A pre-storage treatment with the natural hormone salicylic acid can alleviate chilling damage, although the mechanism is unclear. We found that a treatment with 1 µmol L-1 salicylic acid for 15 min prior to storage at 4 °C delayed and reduced fruit internal browning, a symptom of chilling injury. Salicylic acid had a large effect on sugar metabolism, increasing total soluble sugars via a substantial increase in sucrose content. The transcript abundance of genes related to sucrose biosynthesis and degradation was significantly regulated by salicylic acid, consistent with the changes in sucrose content. Salicylic acid treatment also increased the expression of two DREB cold stress-related proteins, transcriptional activators that regulate cold resistance pathways. The results show that salicylic acid alleviates chilling injury in peach by multiple mechanisms, including an increased content of sucrose and activation of cold response genes.

Effect of Blueberry Anthocyanin-Rich Extracts on Peripheral and Hippocampal Antioxidant Defensiveness: The Analysis of the Serum Fatty Acid Species and Gut Microbiota Profile.

The current study investigated the positive effects of blueberry anthocyanin-rich extracts (BAE) on either peripheral or hippocampal antioxidant defensiveness and established the connection of the improved antioxidant status with the altered fatty acid species and gut microbiota profile. High-fat diet-induced oxidative stress in C57BL/6 mice was attenuated by BAE administration, which was reflected by strengthened antioxidant enzymes, alleviated hepatic steatosis, and improved hippocampal neuronal status. Serum lipidomics analysis indicated that the fatty acid species were altered toward the elevated unsaturated/saturated ratio, along with phospholipid species toward enriched n-3 polyunsaturated fatty acid compositions. The modulated antioxidant pattern could be attributed to the increased bacteria diversity, stimulated probiotics (Bifidobacterium and Lactobacillus) and short-chain fatty acid (SCFA) producers (Roseburia, Faecalibaculum, and Parabacteroides) improved by anthocyanins and their metabolites, which improved the colon environment, characterized by promoted SCFAs, restored colonic mucosa, and reorganized microbial structure. Thus, anthocyanin-rich dietary intervention is a promising approach for the defensiveness in human oxidative damage and neurodegeneration.

Systematic Review of Phenolic Compounds in Apple Fruits: Compositions, Distribution, Absorption, Metabolism, and Processing Stability.

As the most widely consumed fruit in the world, apple (Malus domestica Borkh.) fruits provide a high level of phenolics and have many beneficial effects on human health. The composition and content of phenolic compounds in natural apples differs according to the tissue types and cultivar varieties. The bioavailability of apple-derived phenolics, depending on the absorption and metabolism of phenolics during digestion, is the key determinant of their positive biological effects. Meanwhile, various processing technologies affect the composition and content of phenolic compounds in apple products, further affecting the bioavailability of apple phenolics. This review summarizes current understanding on the compositions, distribution, absorption, and metabolism of phenolic compounds in apple and their stability when subjected to common technologies during processing. We intend to provide an updated overview on apple phenolics and also suggest some perspectives for future research of apple phenolics.

Bioaccessibility of carotenoids and antioxidant capacity of seed-used pumpkin byproducts powders as affected by particle size and corn oil during in vitro digestion process.

Powders made from seed-used pumpkin flesh (SUPF) are potential sources of carotenoids. In this study, unexplored effects of particle size and corn oil on bioaccessible amounts of carotenoids and antioxidant capacity of SUPF powders during in vitro digestion process were investigated. Overall, total carotenoid relative bioaccessibility (TCRB) of 100 mesh-sized powder (100 MP, 15.46%) was higher than that of 18 mesh-sized powder (18 MP, 12.94%). With the addition of 2% corn oil, TCRB increased 108.35% (18 MP) and 88.55% (100 MP), respectively. Lutein (≥27160 µg/100 g) and ß-carotene (≥5192 µg/100 g) were main carotenoid monomers in SUPF and significantly correlated with DPPH radical scavenging activity of digestive supernatant (p < 0.05). Notably, DPPH radical scavenging activity of 18 MP increased 96.54% with corn oil. These results implied that smaller particle size and oil addition could improve bioaccessible amounts of carotenoids and antioxidant capacity of SUPF powders.

Impacts of thermal and non-thermal processing on structure and functionality of pectin in fruit- and vegetable- based products: A review.

Pectin, a major polysaccharide found in the cell walls of higher plants, plays major roles in determining the physical and nutritional properties of fruit- and vegetable-based products. An in-depth understanding of the effects of processing operations on pectin structure and functionality is critical for designing better products. This review, therefore, focuses on the progress made in understanding the effects of processing on pectin structure, further on pectin functionality, consequently on product properties. The effects of processing on pectin structure are highly dependent on the processing conditions. Targeted control of pectin structure by applying various processing operations could enhance textural, rheological, nutritional properties and cloud stability of products. While it seems that optimizing product quality in terms of physical properties is counteracted by optimizing the nutritional properties. Therefore, understanding plant component biosynthesis mechanisms and processing mechanisms could be a major challenge to balance among the quality indicators of processed products.

Inactivation and structural changes of polyphenol oxidase in quince (Cydonia oblonga Miller) juice subjected to ultrasonic treatment.

BACKGROUND: Polyphenol oxidase (PPO) is considered a problem in the food industry because it starts browning reactions during fruit and vegetable processing. Ultrasonic treatment is a technology used to inactivate the enzyme; however, the mechanism behind PPO inactivation is still unclear. For this reason, the inactivation, aggregation, and structural changes in PPO from quince juice subjected to ultrasonic treatments were investigated. Different intensities and times of ultrasonic treatment were used. Changes in the activity, aggregation, conformation, and structure of PPO were investigated through different structural analyses. RESULTS: Compared to untreated juice, the PPO activity in treated juice was reduced to 35% at a high ultrasonic intensity of 400 W for 20 min. The structure of PPO determined from particle size distribution (PSD) analysis showed that ultrasound treatment caused initial dissociation and subsequent aggregation leading to structural modification. The spectra of circular dichroism (CD) analysis of ultrasonic treated PPO protein showed a significant loss of α-helix, and reorganization of secondary structure. Fluorescence analysis showed a significant increase in fluorescence intensity of PPO after ultrasound treatment with evident blue shift, revealing disruption in the tertiary structure. CONCLUSION: In summary, ultrasonic treatment triggered protein aggregation, distortion of tertiary structure, and loss of α-helix conformation of secondary structure causing inactivation of the PPO enzyme. Hence, ultrasound processing at high intensity and duration could cause the inactivation of the PPO enzyme by inducing aggregation and structural modifications. © 2019 Society of Chemical Industry.

Characteristics of cell wall pectic polysaccharides affect textural properties of instant controlled pressure drop dried carrot chips derived from different tissue zone.

To better understanding the role of cell wall pectic polysaccharides (CWPs) on the formation of textural properties of carrot chips dried by instant controlled pressure drop technology (French for Détente Instantanée Contrôlée, DIC), the characteristics of CWPs from ground tissue (GT), junction of ground and vascular tissue (JT), and vascular tissue (VT) of carrot were investigated. Larger expansion volume was obtained in the carrot chips derived from GT, which accompanied with superior textural qualities compared with the chips derived from JT and VT. Remarkable differences were obtained in the amount of pectic fractions, galacturonic acid content, degree of methoxylation, sugar composition and linearity of CWPs that fractionated from different tissue zones of raw carrots. The characteristics of CWPs was confirmed to be a substantial factor that significantly affected the expansion ratio and textural properties of the DIC-dried carrot chips, which providing a mechanistic insight of the relationship between variation in CWPs and the expanding behaviors of DIC-dried fruits and vegetables.

Effects of high pressure homogenization and addition of oil on the carotenoid bioaccessibility of carrot juice.

Food processing and dietary lipids are considered as important factors for carotenoid bioaccessibility. The effects of high pressure homogenization (HPH) combined with oil or emulsion on carotenoid retention and bioaccessibility during digestion were investigated. The results illustrated that HPH decreased the area-based diameter (D[3,2]), and negative correlations were found between the total carotenoid bioaccessibility (TCB) and D[3,2] of carrot juice. The bioaccessibility of total carotenoids, ß-carotene and α-carotene of the homogenized samples was below 6%, while the addition of 2% oil, 10% oil or emulsion increased the carotenoid bioaccessibility (up to 14.08% for α-carotene). The carotenoid retention rate (CRR) of the homogenized samples was higher than that of the homogenized samples with oil or emulsion in each digestion phase. The CRR in the small intestine phase had a significant negative correlation with TCB, and therefore, a high TCB could be achieved despite a low CRR in the small intestine. Oil added as an emulsion had a slightly higher volume of free fatty acids released compared with oil added as such.

Effects of high pressure homogenization on pectin structural characteristics and carotenoid bioaccessibility of carrot juice.

Effects of high pressure homogenization (HPH) on stability, water-soluble pectin (WSP) and total carotenoid bioaccessiblity (TCB) of carrot juice were investigated to reveal the feasibility of applying HPH for improving TCB and the relationships between WSP and TCB induced by HPH. Results illustrated that HPH improved the juice stability and TCB. HPH increased the uronic acid content (UAC), and decreased the degree of methoxylation (DM) and acetylation (DAc) of WSP compared to non-homogenization. However, pressure and pass showed no significant effect on UAC, DM and DAc. HPH decreased the weight-average molar mass of WSP, signifying the degradation, which was enhanced by the increasing pressure. Emulsifying activity (EA) decreased with the increasing pass and inlet temperature. Functional relationships were found between TCB and WSP characteristics (DM and EA). Lower DM and EA contributed to higher TCB. Moreover, statistical correlations were found between TCB and indicators of WSP (UAC and DAc).

Characterization of water status and water soluble pectin from peaches under the combined drying processing.

Characterization of water status and water soluble pectin (WSP) from peach were evaluated after different stage of combined drying in which osmotic dehydration (OD) was considered as the pre-treatment prior to instant controlled pressure drop (DIC) - assisted infrared radiation drying (IRD) (IR-DIC). Results showed that the contents of free water and immobilized water decreased to 0 g after the combined drying. The content of bound water increased after IRD treatment. The residual PME activity in peach slices was 153.3-179.6% after OD treatment, while, the PG were totally inactivated after IRD. The degree of esterification (DE), WSP content and average molar mass (Mw) decreased significantly (from 75.00 to 43.74, from 156.00 to 74.91 mg/g AIR and from 2.28 to 0.49 × 105 Da, respectively) after the combined drying. The neutral sugar of WSP was mainly composed by galactose, arabinose and rhamnose, whose contents decreased after the combined drying. However, OD treatment would slow down the degradation. There was a low peak at 1740 cm-1 in FT-IR spectrum observed for WSP after IRD and DIC treatment, which might illustrate the degradation of WSP during the combined drying.