Development and characterization of cranberry pomace extract incorporated and vitamin E fortified edible films as an edible separation sheet for fruit leather.

The separation sheets for fruit leather are traditionally made of plastic film or wax paper, which not only leads to environmental issues but also is inconvenience to consumers. This study evaluated edible fruit leather separation sheets using food polymers, including hydroxypropyl methyl cellulose (HPMC) and incorporation of cranberry pomace water extract (CPE) for providing natural fruit pigment, flavor, and phenolics. HPMCCPE film was then further improved by incorporating hydrophobic compound (oleic acid, OA) and vitamin E (VE) via cellulose nanocrystal (CNC) Pickering emulsion (CNCP) for enhancing film hydrophobicity and nutritional benefit, respectively. The CNCP-HPMCCPE film exhibited reduced water vapor permeability (∼0.033 g mm/m2 d Pa) compared to HPMCCPE film (∼0.59 g mm/m2 d Pa) and had the least change in mass and moisture content when wrapping fruit leather for up to 2 weeks of ambient storage. The fruit leather wrapped by CNCP-HPMCCPE film showed lower weight change than those by films without CNCP due to low mass transfer between film and fruit leather. CNCP resulted in controlled release of VE into a food simulating solvent (ethanol). The developed colorful and edible fruit leather separation sheet satisfied the increased market demands on sustainable food packaging. PRACTICAL APPLICATION: Colorful and flavorful edible films made of edible polymers, fruit pomace water extract, and emulsified hydrophobic compounds with vitamin E were created. The films have the satisfactory performance to replace the conventional fruit leather separation sheet made of plastic or wax paper. The edible films can be eaten with packaged fruit leather for not only reducing packaging waste but also providing convenience and nutritional benefit to consumers. These functional edible films may also be utilized to package other food products for promoting packaging sustainability and nutritional benefit.

Consumer perception and acceptance of edible packaging for various food products.

Excessive use of single-use plastic packaging presents an imminent threat to the environment. One of the emerging solutions is using edible food packaging. However, there is lack of consumer information toward edible packaging. This study evaluated consumer attitude, acceptability, and purchase intent of three types of edible food packaging: muffin liner, cranberry pomace fruit leather wrap, and powdered drink sachet. One hundred consumers who frequently consumed muffins, strawberry fruit leather, and powdered lemonade were selected from metropolitan area of Portland, Oregon to participate in the study. The panelists were presented with the edible films and the food products with the edible packaging, information card highlighting the environmental-friendly edible package, and were prompted with describing the sensory attributes, purchase intent, and qualities regarding the edible packaging with and without food. Overall, panelists liked the three foods with the edible packaging giving overall liking scores of 7.48, 8.06, and 7.48 for the muffin liners, edible fruit leather wraps, and powdered drink sachets, respectively, based on a 9-point hedonic scale where 1 = dislike extremely and 9 = like extremely. When asked about hypothetical purchase intent, 64%-68% of panelists positively reacted to purchase intent and would buy all three types of edible packaging products. Based on the positive reaction from panelists, edible packaging maybe a possible solution to reducing single-use plastic packaging in the food industry. This study can be the catalyst for further investigation of the efficacy of different applications of edible food packaging as well as consumer perceptions of eating their packaging. PRACTICAL APPLICATION: Edible food packaging is an emerging solution for reducing single-use plastic waste. This study investigated consumer attitude, acceptability, and purchase intent of edible food packaging for three food packaging applications, including edible muffin liner, fruit leather wrap, and powdered drink sachet. This study demonstrated that consumers strongly agree that edible packaging would serve as an environmentally sustainable solution to single-use plastics, and are willing to spend more to purchase these sustainable alternatives. This study provides new information toward the future development of edible packaging and consumer perceptions of eating their packaging.

Development and characterization of cellulose nanofiber reinforced hydroxypropyl methylcellulose films functionalized with propolis-loaded zein nanoparticles and its application for cheddar cheese storage.

Cellulose nanofiber (CNF) reinforced hydroxypropyl methylcellulose (HPMC) films were functionalized with propolis-loaded zein nanoparticles (ZNP) to develop active, printable, and heat-sealable films. The films with 0, 0.10, 0.25, 0.50, or 0.75 mg/mL propolis-loaded ZNP, named 0ZNP, 0.10ZNP, 0.25ZNP, 0.50ZNP, and 0.75ZNP, respectively, were characterized for their mechanical, physicochemical, structural, functional and optical properties and antioxidant activity. The addition of propolis-loaded ZNP did not change tensile strength (P > 0.05), but increased elongation at break (from 24.72 to 36.58 %) (P < 0.05) for 0.25ZNP film. A water contact angle increased significantly (P < 0.05) for 0.50ZNP (~45 %) and 0.75ZNP (~137 %) films. The 0.25ZNP and 0.75ZNP films were evaluated for packaging cheddar cheese under refrigerated storage for 30 days, and resulted in comparable water activity, pH, titratable acidity, and lipid oxidation (P > 0.05) with those packaged by LDPE film and vacuum package. The developed films can function as eco-friendly alternatives to single-use plastic food packaging.

Investigation of a lignocellulose fiber hornification treatment for improving the functionality of apple pomace-based pulp for molded pulp packaging.

Transfer molded pulp packaging (TMPP) is a viable alternative to single use plastic packaging. TMPP is typically produced from recycled newspapers, but the availability of this feedstock material is declining. Apple pomace (AP) pulp, primarily composed of cellulose, hemicellulose, lignin, and pectin, can be used as the primary component of TMPP, but its high water retention value (WRV) and separation from other pulps (recycled cardboard (CB) in this study) limits its utilizations in TMPP. A pressing and thermal drying cellulose hornification treatment followed by a repulping step was implemented to reduce pulp WRV and enhance AP and CB fiber entanglements. 11 %, 20 %, and 25 % reductions in WRV were achieved through 1 t-force pressing and drying at 120 °C for 2.5, 15, or 27.5 min, named mild, medium, and strong hornification treatments, respectively. Increased AP and CB fiber entanglements were observed via microscopy with rising hornification drying times. The medium hornification treatment was identified as the optimal treatment for reducing pulp WRV and reducing pulp separation without decreasing pulp sheet tensile strength. This study introduced and validated a novel processing technique for improved functionality of AP-based pulp for packaging applications.

Evaluation of Functional Spray Coatings for Mitigating the Uptake of Volatile Phenols by Pinot Noir Wine Grapes via Blocking, Absorption, and/or Adsorption.

Spray coatings have shown promising potential in preventing the uptake of smoke phenols from wildfires into wine grapes. Three cellulose nanofiber-based coatings with low methoxyl pectin or varying concentrations of chitosan were made into films and their potential for blocking, absorption, or adsorption of phenols (guaiacol, m-cresol, and syringol) was evaluated using a custom-built smoke diffusion box. The coatings were also applied to Pinot noir grapes in a vineyard. GC-MS analysis for smoke phenols from headspace gases of diffusion study and extractions of films indicated that chitosan-based films can block guaiacol and syringol, and all films are able to capture m-cresol. The type of coating and application time in a vineyard did not affect (P < 0.05) physicochemical properties, size, and weight of the berries, whereas chitosan-based coatings resulted in a higher anthocyanin content of berries. This study provided new information about the key mechanisms (i.e., blocking phenols) of coatings to mitigate smoke phenol uptake in wine grapes.

Impact of functional spray coatings on smoke volatile phenol compounds and Pinot noir grape growth.

The frequency and intensity of wildfires have been increasing over the last 50 years and negatively impacted the wine industry. Previous methods of smoke mitigation during grape processing have shown little impact in reducing smoke taint in wines. Therefore, a novel method of using edible spray coatings for vineyard application was developed to help prevent volatile smoke phenol uptake in wine grapes. Four cellulose nanofiber-based coating suspensions incorporated with chitosan and/or ß-cyclodextrin were evaluated. Films derived from the coating suspensions were exposed to volatile phenols found in wildfire smoke (guaiacol, 4-methyl guaiacol, m-cresol, o-cresol, p-cresol, syringol, and 4-methyl syringol) and evaluated with ultraviolet-visible spectroscopy where the results indicated that the coatings could uptake smoke phenols in varying degrees. The coatings were also applied in a vineyard at three different application times during grape growth: pea-sized, pre-bunch closure, and both at pea-sized and pre-bunch closure. The results showed that the application time did not have a significant (p < 0.05) effect on berry size, weight, °Brix, pH, or titratable acidity. The type of coating, time of application and washing were found to impact the number of volatile phenols in the grapes after a smoke event. Results from this study indicated that edible coatings could help mitigate smoke uptake in wine grapes without sacrificing the growth and key composition parameters of wine grapes. PRACTICAL APPLICATION: This research provides a novel spray coating that can be applied to wine grapes in the vineyard to potentially mitigate volatile smoke compounds in wine grapes without impacting fruit growth and key compositional parameters of wine grapes, thus maintaining high quality of wines for consumers. Results from this study can also be potentially applied to other agricultural commodities to solve the issues caused by the wildfire smoke.

Enhancing anthocyanin-phenolic copigmentation through epicarp layer treatment and edible coatings to retain anthocyanins in thermally processed whole blueberries.

Anthocyanins in processed fruit degrade significantly due to their heat and oxygen sensitivity and water solubility. Copigmentation for stabilizing anthocyanins is less effective for whole fruit due to anthocyanins' location within cell vacuoles surrounded by the epicarp layer as barrier to prevent copigment complexing with anthocyanins. This study investigated strategies for enhancing anthocyanin-phenolic copigmentation on blueberry surface, and integrated copigmentation with layer-by-layer (LBL) coating to retain anthocyanin stability in thermally processed blueberries. Results indicated that epicarp layer treatment of fruit by Tween 80 (T80) and CaCl2 is important for enhancing anthocyanin-phenolic copigmentation. The sequential copigmentation treatment using T80, ferulic acid, and CaCl2 (T80→FA→CaCl2 ) or T80, tannic acid, and CaCl2 (T80→TA→CaCl2 ) resulted in higher (p < 0.05) retention of total monomeric anthocyanin (3.18 mg/g and 3.38 mg/g, respectively) in thermally processed blueberries after 7-day ambient storage than that of untreated fruit (2.79 mg/g). Percent polymeric color (PPC) of blueberries treated by T80→FA→CaCl2 (15.5%) or T80→TA→CaCl2 (17.4%) was lower (p < 0.05) than that treated by TA alone (22.5%). The LBL coating enhanced microstructure stability for preserving anthocyanins in thermally processed blueberries. This study demonstrated the effectiveness of sequential copigmentation of blueberries after epicarp layer treatment followed by LBL coating for enhancing anthocyanin stability in processed whole fruit. PRACTICAL APPLICATION: When anthocyanin-rich fruit is thermally processed, anthocyanins degrade and leach to aqueous packing solution because of its heat sensitivity and water solubility. This study developed an innovative technology through implementing sequential treatments of copigmentation and water- and heat-resistant coating for preventing heat and water degradation of anthocyanins in whole fruit during processing in aqueous media. The developed technology can be practically applied to enhance the quality and health benefits of thermally processed anthocyanin-rich whole fruit. The technology can not only be utilized to improve existing fruit products, but also develop new and novel fruit products.

Mechanisms and performance of cellulose nanocrystals Pickering emulsion chitosan coatings for reducing ethylene production and physiological disorders in postharvest 'Bartlett' pears (Pyrus communis L.) during cold storage.

Pickering emulsion coating (CNCP-CH) composed of oleic acid (OA, 1, 2, and 3%, w/w), cellulose nanocrystal (CNC, 0.1, 0.3, and 0.5%, w/w), and 2% chitosan (CH) was optimized for high emulsion stability. It was found that OA concentration played significant role on emulsion stability. Increasing OA from 1 to 3% reduced emulsion stability ~43%, indicated by the thickness of separated cream layer in the emulsion. 'Bartlett' pears (Pyrus communis L.) coated by CNCP-CH containing 1% OA showed significantly reduced ethylene production than that coated with 2% and 3% OA at 1-month of accelerated cold storage at 1.7 °C. The superficial scald on pear peels was only observed on fruit coated by CNCP-CH with 3% OA, but not that with 1% or 2% OA. Therefore, CNCP-CH coating with 1% OA, 0.1% CNC, and 2% CH was suggested for delaying ripening and superficial scald of 'Bartlett' pears during the long-term cold storage.

Quality and Consumer Acceptance of Berry Fruit Pomace-Fortified Specialty Mustard.

Blueberry pomace (BP) and cranberry pomace (CP) are good sources of dietary fiber and phenolics. This study aimed to develop berry fruit pomace (FP)-fortified specialty mustard with elevated bioactive compounds and ascertain consumer acceptance of a new product. Wet BP and CP were ground and incorporated into Dijon-style mustard at concentrations of 15%, 20%, and 25% (w/w). Total dietary fiber (TDF), total phenolic content (TPC), and radical scavenging activity (RSA) were evaluated for samples obtained from both chemical extraction (CE) and simulated gastrointestinal digestion (SGD). Physicochemical properties and consumer acceptance were also examined. Increasing concentrations of BP or CP significantly increased TDF of mustards from both CE (AOAC methods) and SGD, with the highest values from 25% fortifications. TDF from AOAC ranged from 26.86% to 40.16% for BP and from 26.86% to 38.42% for CP, while TDF from SGD ranged from 31.02% to 42.68% for BP and 31.02% to 63.65% for CP. From CE, no significant variation of TPC was found, but RSA significantly increased with increasing concentration of BP and CP. TPC from SGD was higher than that from CE, where TPC decreased with increasing concentration of BP or CP. RSA from SGD was lower than that from CE. Sensory scores of pomace-fortified samples were significantly lower than the control; however, informed panelists scored BP-fortified mustard significantly higher on appearance and color liking than uninformed panelists. This study demonstrated that with proper marketing, the utilization of FP in condiments is a viable option for potential health benefits. PRACTICAL APPLICATION: This research is applicable to multiple areas of the food industry. Juice manufacturers or other companies that process raw agricultural produce can use this research as another way to repurpose biowaste, and companies making specialty condiments can use this research to inform future product development. General considerations discussed regarding the use of berry fruit pomace can be applied by any company interested in pomace reuse.

Moisture Adsorption Isotherm and Storability of Hazelnut Inshells and Kernels Produced in Oregon, USA.

Moisture adsorption isotherms and storability of dried hazelnut inshells and kernels produced in Oregon were evaluated and compared among cultivars, including Barcelona, Yamhill, and Jefferson. Experimental moisture adsorption data fitted to Guggenheim-Anderson-de Boer (GAB) model, showing less hygroscopic properties in Yamhill than other cultivars of inshells and kernels due to lower content of carbohydrate and protein, but higher content of fat. The safe levels of moisture content (MC, dry basis) of dried inshells and kernels for reaching kernel water activity (aw ) ≤0.65 were estimated using the GAB model as 11.3% and 5.0% for Barcelona, 9.4% and 4.2% for Yamhill, and 10.7% and 4.9% for Jefferson, respectively. Storage conditions (2 °C at 85% to 95% relative humidity [RH], 10 °C at 65% to 75% RH, and 27 °C at 35% to 45% RH), times (0, 4, 8, or 12 mo), and packaging methods (atmosphere vs. vacuum) affected MC, aw , bioactive compounds, lipid oxidation, and enzyme activity of dried hazelnut inshells or kernels. For inshells packaged at woven polypropylene bag, MC and aw of inshells and kernels (inside shells) increased at 2 and 10 °C, but decreased at 27 °C during storage. For kernels, lipid oxidation and polyphenol oxidase activity also increased with extended storage time (P < 0.05), and MC and aw of vacuum packaged samples were more stable during storage than those atmospherically packaged ones. Principal component analysis showed correlation of kernel qualities with storage condition, time, and packaging method. This study demonstrated that the ideal storage condition or packaging method varied among cultivars due to their different moisture adsorption and physicochemical and enzymatic stability during storage. PRACTICAL APPLICATION: Moisture adsorption isotherm of hazelnut inshells and kernels is useful for predicting the storability of nuts. This study found that water adsorption and storability varied among the different cultivars of nuts, in which Yamhill was less hygroscopic than Barcelona and Jefferson, thus more stable during storage. For ensuring food safety and quality of nuts during storage, each cultivar of kernels should be dried to a certain level of MC. Lipid oxidation and enzyme activity of kernel could be increased with extended storage time. Vacuum packaging was recommended to kernels for reducing moisture adsorption during storage.

Cellulose nanomaterials emulsion coatings for controlling physiological activity, modifying surface morphology, and enhancing storability of postharvest bananas (Musa acuminate).

Cellulose nanomaterials (CNs)-incorporated emulsion coatings with improved moisture barrier, wettability and surface adhesion onto fruit surfaces were developed for controlling postharvest physiological activity and enhancing storability of bananas during ambient storage. Cellulose nanofiber (CNF)-based emulsion coating (CNFC: 0.3% CNF/1% oleic acid/1% sucrose ester fatty acid (w/w wet base)) had low contact angle, high spread coefficient onto banana surfaces, and lower surface tension (ST, 25.4mN/m) than the critical ST (35.2mN/m) of banana peels, and exhibited good wettability onto banana surfaces. CNFC coating delayed the ethylene biosynthesis pathway and reduced ethylene and CO2 production, thus delaying fruit ripening. As the result, CNFC coating minimized chlorophyll degradation, weight loss, and firmness of bananas while ensuring the properly fruit ripening during 10d of ambient storage. This study demonstrated the effectiveness of CNF based emulsion coatings for improving the storability of postharvest bananas.

Cellulose Nanocrystal Reinforced Chitosan Coatings for Improving the Storability of Postharvest Pears Under Both Ambient and Cold Storages.

Cellulose nanocrystal (CNC, 0%, 5%, and 10% w/w, in chitosan, dry basis) reinforced 2% chitosan aqueous coatings were evaluated for delaying the ripening and quality deterioration of postharvest green D'Anjou (Pyrus communis L.) and Bartlett (Pyrus communis L.) pears during 3 wk of ambient storage (20 ± 2 °C and 30 ± 2% RH) or 5 mo of cold storage (-1.1 °C and 90% RH), respectively. Ethylene and CO2 production, color, firmness, and internal fruit quality were monitored during both storage conditions. Moisture and gas barrier, antibacterial activity, and surface morphology of the derived films were also evaluated to investigate the mechanisms of delayed fruit ripening and quality deterioration. In the ambient storage study, the 5% CNC reinforced chitosan coating significantly (P < 0.05) delayed green chlorophyll degradation of pear peels, prevented internal browning, reduced senescence scalding, and improved retained fruit firmness. During cold storage, the 5% CNC reinforced chitosan coating showed a competitive effect on delaying fruit postharvest quality deterioration compared to a commercial product (Semperfresh™, Pace International, Wapato, Wash., U.S.A.). The 5% CNC coating strongly adhered to the pear surface, provided a superior gas barrier and a more homogenous matrix in comparison with the other coatings tested. Hence, it was effective in delaying ripening and improving the storability of postharvest pears during both ambient and cold storage.

Chitosan-cellulose nanocrystal microencapsulation to improve encapsulation efficiency and stability of entrapped fruit anthocyanins.

For improving stability of fruit anthocyanins (ACN), this study investigated the use of cellulose nanocrystal (CNC) as a macroion crosslinking agent to develop blueberry anthocyanin extract (BB)-loaded chitosan (CH)-CNC microcapsules, and compared with CH-sodium tripolyphosphate (TPP) ones. The yield of microcapsules (∼6.9g) and total monomeric anthocyanin recovery (∼94%) were significantly (P<0.05) higher in CH-CNC microcapsules than those (∼0.3g and ∼33%, respectively) in CH-TPP microcapsules. ACN distribution (%) in CH-CNC microcapsules was 61% on the surfaces, 12% bound with the matrix, and 27% in cores, but that in CH-TPP microcapsules was mostly presented on the surfaces (99%). CH-CNC microcapsules were more stable at pH 7.4 buffer by showing less ACN release (%) than that of CH-TPP, but no difference at pH 1.2. CH-CNC and CH-TPP microcapsules showed different structural and morphological properties. This study demonstrated that CNC is a promising crosslinking agent forming stable BB-loaded CH microcapsules.

Preparation, characterization and evaluation of antibacterial activity of catechins and catechins-Zn complex loaded ß-chitosan nanoparticles of different particle sizes.

This study used ß-chitosan nanoparticles (ß-CS NPs) of different particle sizes to encapsulate catechins (CAT) or CAT-Zn complex by ionic gelation technology. The antibacterial activity of CAT or CAT-Zn complex loaded ß-CS NPs against Escherichia coli and Listeria innocua were investigated based on bacterial growth curve, minimum inhibitory concentration (MIC), and minimum bacterial concentration (MBC). Fourier transform infrared spectrometer (FT-IR) was employed to study the incorporation of CAT or CAT-Zn complex into ß-CS NPs. The CAT-Zn complex loaded ß-CS NPs had particle size of 208-591 nm, polydispersity index (PDI) of 0.377-0.395, and positive Zeta-potential of 39.17-45.62 mV. The CAT-Zn complex loaded ß-CS NPs of smaller particle sizes showed higher antibacterial activity than that of larger particle size ones. The MIC and MBC of CAT-Zn complex loaded ß-CS NPs of the smallest particle size against L. innocua and E. coli were 0.031 and 0.063 mg/mL, and 0.063 and 0.125 mg/mL, respectively. This study suggested that encapsulation of CAT-Zn complex in ß-CS NPs improved the antibacterial activity of CAT and CAT-Zn complex, and the encapsulators have great potential to be used as antibacterial substances for food and other applications through either direct addition or incorporation into packaging materials.

Impingement drying for preparing dried apple pomace flour and its fortification in bakery and meat products.

This study aimed to evaluate impingement drying (ID) as a rapid drying method to dry wet apple pomace (WAP) and to investigate the fortification of dried apple pomace flour (APF) or WAP in bakery and meat products. ID at ~110 °C reduced the moisture content of apple pomace from 80 % (wet basis) to 4.5 % within 3 h, compared with 24 h to 2.2 % using 40 °C forced-air drying and ~60 h to 2.3 % using freeze drying. Furthermore, ID enhanced the extractable phenolic compounds, allowing for a 58 % increase in total phenolic content (TPC) compared with wet pomace, a 110 % and 83 % higher than TPC in forced-air dried and freeze dried samples, respectively. The 15-20 % APF-fortified cookies were found to be ~44-59 % softer, ~30 % more chewy, and ~14 % moister than those of the control. WAP-fortified meat products had significantly higher dietary fiber content (0.7-1.8 % vs. 0.1-0.2 % in control) and radical scavenging activity than that of the control. These results suggest that impingement drying is a fast and effective method for preparing dried APF with highly retained bioactive compounds, and apple pomace fortified products maintained or even had improved quality.

Investigation of the mechanisms of using metal complexation and cellulose nanofiber/sodium alginate layer-by-layer coating for retaining anthocyanin pigments in thermally processed blueberries in aqueous media.

This study investigated the mechanisms of anthocyanin pigment retention using Fe(3+)-anthocyanin complexation and cellulose nanofiber (CNF)/sodium alginate (SA) layer-by-layer (LBL) coatings on thermally processed blueberries in aqueous media. Anthocyanin pigments were polymerized through complexation with Fe(3+) but readily degraded by heat (93 °C for 7 min) in the aqueous media because of poor stability. CNF/SA LBL coating was successful to retain anthocyanin pigments in thermally processed blueberries. Fruits coated with CNF containing CaCl2 followed by treatment in a SA bath formed a second hydrogel layer onto the CNF layer (LBL coating system) through cross-linking between Ca(2+) and alginic acid. Methyl-cellulose-modified CNF improved the interactions between CNF, the fruit surface, and the SA layer. This study demonstrated that the CNF/SA LBL coating system was effective to retain anthocyanin pigments on thermally processed whole blueberries, whereas no combined benefit of complexation with coating was observed. Results explained the mechanisms of the new approaches for developing colorful and nutritionally enhanced anthocyanin-rich fruit products.

Impact of acidity and metal ion on the antibacterial activity and mechanisms of ß- and α-chitosan.

This study investigated the effects of acidity and metal ion on the antibacterial activity of α- and ß-chitosan at different molecular weights (Mw, 22-360 kDa) against Escherichia coli and Listeria innocua through agar well diffusion assay. Spectrophotometric, electrophoretic, and confocal fluorescence microscopy analysis were further employed to evaluate the antibacterial mechanisms probably involved. Increasing pH from 4.0 to 5.0 weakened the antibacterial ability of chitosan as shown by the decreased bacteria growth inhibition zone (BGIZ) from 0.63 to 0.57 cm for ß-chitosan (61 kDa) and from 0.62 to 0.57 cm for α-chitosan (30 kDa) against E. coli. All ß- and α-chitosan samples showed antibacterial activity against L. innocua, in which 22 kDa ß-chitosan and 30 kDa α-chitosan at pH 4.0 had the highest antibacterial activity with BGIZ of 1.22 and 0.98 cm, respectively. Interactive effect between pH and Mw on the antibacterial activity of ß-chitosan was observed, but not of α-chitosan. Adding Co(2+) and Ni(2+) significantly improved the antibacterial activity of chitosan, while adding K(+), Na(+), and Li(+) significantly weakened the antibacterial activity of some ß- and α-chitosan samples (P < 0.05), and different Mw and forms of chitosan showed different metal ion absorption capacities. Results indicate that chitosan might insert into the groove of bacterial DNA double helix structure to induce DNA degradation and permeate through bacteria cell membranes and combine with genomic DNA to induce its dysfunction, providing evidences for the antibacterial mechanisms of chitosan.

Alkali- or acid-induced changes in structure, moisture absorption ability and deacetylating reaction of ß-chitin extracted from jumbo squid (Dosidicus gigas) pens.

Alkali- or acid-induced structural modifications in ß-chitin from squid (Dosidicus gigas, d'Orbigny, 1835) pens and their moisture absorption ability (MAA) and deacetylating reaction were investigated and compared with α-chitin from shrimp shells. ß-Chitin was converted into the α-form after 3h in 40% NaOH or 1-3 h in 40% HCl solution, and α-chitin obtained from NaOH treatment had higher MAA than had native α-chitin, due to polymorphic destructions. In contrast, induced α-chitin from acid treatment of ß-chitin had few polymorphic modifications, showing no significant change (P>0.05) in MAA. ß-Chitin was more susceptible to alkali deacetylation than was α-chitin, and required a lower concentration of NaOH and shorter reaction time. These results demonstrate that alkali- or acid-treated ß-chitin retained high susceptibility toward solvents, which in turn resulted in good biological activity of ß-chitosan for use as a natural antioxidant and antimicrobial substance or application as edible coatings and films for various food applications.