Synthesis and swelling properties of poly[acrylamide-co-(crotonic acid)] superabsorbents

Superabsorbent polymers of acrylamide (AAm)/crotonic acid (CA) were synthesized by foamed polymerization in an aqueous solution of AAm with CA as a comonomer, initiated by an initiator couple of ammonium persulfate and N,N,N′N′-tetramethylethylenediamine. A crosslinking agent N,N′-methylenebisacrylamide, a foaming agent sodium bicarbonate, and a foam stabilizer, a triblock copolymer of polyoxyethylene/polyoxypropylene/polyoxyethylene, were used in the polymerization. The influences of the relative contents of CA, crosslinking agent, and initiator, on the swelling properties of the superabsorbent polymer systems were examined. The superabsorbent polymer synthesized with an AAm/CA ratio of 98:2 by mole, 0.5 wt.% of N,N′-methylenebisacrylamide and 1 wt.% of ammonium persulfate at 250 rpm and 50 °C for 30 min of polymerization time produced the highest water absorption of 211 ± 9 times its dried weight and could absorb water up to 162 ± 4 g g⁻¹ of the dry copolymer within 10 min. The electrochemical reaction for acrylamide–crotonic acid polymerization was investigated by cyclic voltammetry. The anodic current indicated that acrylamide acting as an electron donor whereas crotonic acid performed as an electron receiver, then providing the cathodic current. The diffusion of water into the superabsorbent polymer was non-Fickian (case II and anomalous). Acrylamide–crotonic acid superabsorbents containing various crosslinker concentrations had a water swelling in the range of 79–289 g g⁻¹. The diffusion coefficients varied between 6.9 × 10⁻⁹ and 5.1 × 10⁻⁸ cm² s⁻¹. Adsorption of the basic dye by the superabsorbent was a monolayer evaluated by the Langmuir isotherm. The superabsorbents can thus be used to adsorb cationic dyes in textile industry.     

大豆种皮多糖在甘露聚糖酶修饰下力学行为的演变

利用β-甘露聚糖酶限制性水解大豆种皮多糖,探讨不同水解时间对大豆种皮多糖流变性质及凝胶强度的影响。结果表明:随着β-甘露聚糖酶作用时间的延长,多糖粘度有下降趋势;酶修饰对胶凝行为的影响则更复杂,修饰作用表现出时间依赖性,在不同的处理时间,多糖的力学行为给予各自独特的响应,原因可能是酶处理时间不同,从多糖分子中游离出来的单糖及寡糖组分的区别造成了分子间相互作用及对环境响应的差异,进而影响多糖分子的力学行为。     

贮藏温度对大平顶枣品质的影响

为探究贮藏环境对大枣品质的影响,以朝阳大平顶枣为原料,在0℃、4℃、10℃、20℃温度下进行贮藏试验。通过测定贮藏过程中失重率、硬度、还原糖含量、可滴定酸含量的变化。结合低场核磁共振技术测定贮藏中水分的迁移,研究大枣的水分动态s变化的微观过程。结果表明:0℃和4℃低温贮藏能显著延缓大枣硬度的变化,抑制大枣贮藏期间失重率的增加。随着贮藏温度的降低,还原糖含量开始下降的时间延后。贮藏35 d时,0℃贮藏的大枣中可滴定酸含量分别比4℃、10℃、20℃的含量高9.90%、44.10%、54.50%。采用低场核磁共振技术检测大枣中水分迁移情况,测得自由水幅度下降顺序为20℃>10℃>4℃>0℃,温度越高,自由水在贮藏中的损失越多,下降的速率越快,从微观角度初探了大枣贮藏过程中变化机理。     

超高压处理对冷藏鲈鱼品质的影响

研究了不同超高压条件(0、100、200、300 MPa,保压处理10 min)对鲈鱼冷藏过程中感官、p H值、白度、质构特性和持水性的影响。结果表明:鱼肉的感官评分、硬度、弹性和咀嚼度随贮藏时间的延长逐渐降低,白度逐渐升高,p H值先下降后上升,而持水性先上升后下降。超高压处理可显著提高鱼肉的硬度和咀嚼度(P0.01),同时提高了鱼肉的p H值和持水能力,增加了白度,200 MPa处理组的细菌总数低于对照组和其他2个处理组。此外,300 MPa的超高压处理对鲈鱼鱼肉品质的影响最大。综合感官和理化测定结果可知,超高压在改善鲈鱼肉质方面具有潜在的应用前景。     

Effect of tea polyphenols on the physical and chemical characteristics of dried-seasoned squid (Dosidicus gigas) during storage

The effects of tea polyphenols (TP) dip treatment on the physical and chemical characteristics of dried-seasoned squid (Dosidicus gigas) during storage at 25 °C were assessed. After the storage, the b* value increased significantly, while the free amino acids (FAA) including Ser, Gly, Arg, Tyr and Lys, and the dominant reducing sugar (RS), lactose, decreased remarkably, which revealed the occurrence of browning reaction in dried-seasoned squid. The progressive conversion of trimethylamine oxide (TMAO) and production of thiobarbituric acid (TBA) and total volatile basic nitrogen (TVB-N) were found during the entire period of storage. Furthermore, the advantages of reducing moisture loss, inhibiting oxidation of lipids, depressing TMAO breakdown and TVB-N accumulation were observed, while the browning reaction exhibited no significant decrease for the TP samples. These results indicated that the addition of TP could maintain quality of dried-seasoned squid.     

薄膜梯度扩散-石墨炉原子吸收光谱法测定自来水中痕量Cd（Ⅱ）

建立薄膜梯度扩散（diffusive gradients in thin-films,DGT）富集-石墨炉原子吸收光谱（graphite furnace atomicabsorption spectrometry,GFAAS）法测定自来水中痕量Cd（Ⅱ）的新方法。先以聚天冬氨酸溶液为结合相的DGT装置富集自来水中Cd（Ⅱ）,再使用GFAAS测定DGT结合相中Cd（Ⅱ）的含量,最后依据DGT方程计算自来水中Cd（Ⅱ）质量浓度。DGT-GFAAS法测得配制水中Cd（Ⅱ）的回收率为96.2%～101.7%;测得自来水中Cd（Ⅱ）质量浓度为0.21～0.35 mg/L,加标回收率为95.4%～107.0%,相对标准偏差为3.7%～7.4%;DGT-GFAAS法对自来水中Cd（Ⅱ）的检出限为0.002 5 μg/L（采样48 h）,可应用于饮用水中痕量Cd（Ⅱ）的定量测量。     

蓝莓叶多酚对冷藏鲈鱼品质的影响

目的:研究蓝莓叶多酚对冷藏鲈鱼品质的影响,为鲈鱼的生物保鲜提供新方法。方法:用4 mg/m L蓝莓叶多酚浸泡鲈鱼,以感官特征、菌落总数、pH值、TBA、TVB-N、K值为评价指标,研究蓝莓叶多酚对4℃冷藏鲈鱼的保鲜效果。结果:蓝莓叶多酚在鲈鱼冷藏保鲜过程中能有效控制鲈鱼品质,抑制细菌繁殖,减缓脂肪氧化,比对照组延长鲈鱼货架期4~5 d。结论:蓝莓叶多酚是有效的食品生物保鲜剂。     

抗真菌性乳酸菌生物保护剂的研究进展

霉菌和酵母不仅引起果蔬、谷类、乳制品和肉制品等食品及农产品腐败变质,造成巨大的经济损失,而且霉菌还产生有害于人体健康的黄曲霉毒素、伏马菌素、单端孢霉烯、赭曲霉素A和棒曲霉素等真菌毒素,给食用者带来潜在的食品安全隐患。随着消费者对鲜活和微加工食品的需求不断增加,化学防腐剂在食品中应用受到限制,食品生物保护剂研究及应用已成为热点。乳酸菌通过生态位竞争、形成酸性环境和产生各种代谢产物对致病菌和腐败微生物具有较强的拮抗作用,作为一新型生物保护剂已广泛应用于各种食品中。本文对食品中抗真菌性乳酸菌的筛选和应用、乳酸菌产生的抗真菌代谢产物以及发展趋势进行综述,为进一步探究乳酸菌抗菌机理,研发高效食品生物保护剂提供借鉴与参考。     

紫菜多糖提取物对冷藏对虾品质的影响

对虾营养丰富,但极易腐败变质,为研究紫菜多糖提取物对冷藏对虾品质的影响,延长冷藏对虾的货架期。本文将0.8%紫菜多糖处理的对虾和对照组贮存在(4±1)℃的冰箱中8d,在第0、2、4、6、7和8d进行品质评价。通过测定生物指标(菌落总数)、化学指标(pH值、挥发性盐基氮(TVB-N)、硫代巴比妥酸(TBA)值和K值)和感官评分来评价冷藏过程中对虾的品质变化。结果表明,紫菜多糖处理的对虾,在冷藏过程中细菌总数、pH值、TVB-N、TBA值和K值显著低于对照组,感官评分也显著低于对照组。紫菜多糖处理的对虾相对对照组延长货架期3~4d。紫菜多糖提取物在对虾冷藏保鲜过程中能有效抑制细菌繁殖,减缓脂肪氧化,延长对虾的货架期,在对虾冷藏保鲜中具有良好的应用前景。     

酶制剂在果蔬汁澄清及加工中的应用研究进展

当前我国果蔬汁工业迅猛发展,因酶制剂可解决果蔬汁加工中出汁率低、澄清难、易褐变、风味物质易流失和苦味物质难去除等问题,在该领域中得到广泛的应用。目前在果蔬汁加工中应用的酶制剂主要有果胶酶、纤维素酶、淀粉酶、葡萄糖氧化酶、柚苷酶等。本文介绍了果胶酶、纤维素酶、淀粉酶等常见酶制剂在提高果蔬出汁率方面的作用机制及应用进展,比较了酶制剂与其他方法对果蔬汁澄清效果的差异,陈述了葡萄糖氧化酶、柚苷酶、β-葡萄糖苷酶等在改善果蔬汁感官品质方面的应用现状。在分析酶制剂在果蔬汁加工中存在问题的基础上,对酶制剂的应用前景和发展方向进行了展望,为酶制剂在果蔬汁行业的应用提供进一步的依据和参考。