Combined effect of high pressure treatment and anti-microbial bio-sourced materials on microorganisms' growth in model food during storage

Antimicrobial bio-sourced films based on poly(lactic acid) containing either carvacrol or allyl isothiocyanate (AITC) were prepared and their antimicrobial properties were assessed on Botrytis cinerea during storage and after a high pressure (HP) “pasteurisation-like” treatment (up to 800 MPa at ambient temperature). A dry process (extrusion + thermomoulding) was used to shape the material. The high temperature encountered during film processing dramatically decreased the carvacrol and AITC content in the film, leading to a less efficient antimicrobial activity. The use of β-cyclodextrin (β-CD) to encapsulate the active compounds before film processing proved to be efficient to protect the AITC against thermal degradation and to control its release from the films during its use. PLA-based films containing either AITC or β-CD encapsulated AITC showed a significant activity against B. cinerea. An effective combination between the antimicrobial activity of AITC-based films and the high pressure treatment was observed on a model food system (PDA) inoculated with N × 10⁴ (N ~ 1–9) conidia of B. cinerea. An HP treatment of only 300 MPa associated with an antimicrobial PLA/β-CD system providing an initial quantity of active agents equivalent to 4 mg of AITC/L of air (i.e. almost 2 folds lower than the minimal inhibition concentration of the active packaging used alone, which was determined to be equal to 10 mg/L of air in the same conditions) was found more efficient (total inhibition of B. cinerea growth during 10 days) than an 800 MPa HP treatment used alone (increase of the lag phase growth of 3.3 days).

Industrial relevance

The consumer demand for “fresh like” product containing reduced amount of preservatives without compromising human and environmental safety needs the development of new preservation strategies. As a consequence, the concept of “hurdle technologies” has risen up. The combined effect of HP treatment and volatile antimicrobial packaging allowed the use of lower individual treatment intensities to inhibit B. cinerea growth. Combining such “hurdles” is of relevance in the context of development of low-cost and eco-friendly food technologies.     

Lutein: a valuable ingredient of fruit and vegetables

Lutein is a human serum carotenoid which is not synthesized by humans and thus must be obtained by the ingestion of food containing it such as fruits and vegetables. Lutein is present in different forms in those foods as all-trans-lutein, cis-lutein, epoxi-lutein, and lutein linked to proteins. It discusses if the intake of lutein or diets supplemented with lutein or diets rich in fruits and vegetables are important in the prevention of diseases like some cancers, cardiovascular diseases, etc., that may be affected by the antioxidant effect of lutein; or in the prevention of age-related macular degeneration and other eye diseases. The concentration of lutein in fruits and vegetables depends on the species. We've included the concentration of lutein in 74 species reported by different authors since 1990. Currently the quantification of lutein is mainly performed by HPLC, but more investigations into a quantification method for lutein, lutein isomers, and epoxi-lutein are necessary. Improvement of lutein extraction methods is important as well. Methods commonly used in the vegetable and fruit industry like heat treatment, storage conditions, etc. can change lutein concentrations; other factors depend on the plant, for instance the variety, the stage of maturity, etc.     

鳀鱼蒸煮液陶瓷膜微滤浓缩的研究

本文研究了压力、温度、陶瓷膜孔径、蒸煮液浓度和投料方式对微滤浓缩鳀鱼蒸煮液膜通量的影响。微滤浓缩时,0.45 μm和0.14 μm陶瓷膜对蛋白质的浓缩效率相同,但选用0.14 μm陶瓷膜使整体膜浓缩效率提高;升高温度、压力等均能提高陶瓷膜通量;降低蒸煮液的浓度虽能增大陶瓷膜通量,但降低了蛋白质的浓缩效率。45 ℃浓缩时陶瓷膜通量较高,并且浓缩液的菌落总数、挥发性盐基氮（TVB-N）相对于浓缩因子的增长率最小,丙二醛（TBARS）的增长率与35 ℃、25 ℃相近。因此在温度45 ℃、压力0.3 MPa和选用0.14 μm陶瓷膜的条件下,采用间歇的投料方式作为陶瓷膜浓缩鳀鱼蒸煮液较优的操作条件。陶瓷膜清洗方面,复合清洗剂（1% NaOH+0.05% SDS）在45 ℃的清洗条件下,清洗40 min可使膜通量回复率达到98.99%,比单一清洗剂（1% NaOH）提高22.85%。     

用于醋酸菌营养盐的废酵母自溶液研究

为进一步降低醋酸的生产成本,考察并优化了酵母自溶的影响因素与条件,探索采用廉价的废酵母水解液作为有机氮源替代酵母浸粉的可行性。结果表明,自溶反应的最佳条件为加水量200%,初始pH7,0,自溶温度50℃,食盐添加量3%,时间48h。进一步以酵母自溶液对醋酸菌进行摇瓶培养,结果表明,当以酵母自溶液替代酵母浸粉时,醋酸菌浓度的提高超过54%,醋酸含量的提高超过10%。     

高浓度醋的生产工艺概述

近年来,食醋的保健功能日益受到重视.在醋豆、醋蛋液等保健品的制作过程中食醋的选择非常重要,对功效的影响很大,最好使用发酵食品--9度米醋.从发酵技术的角度对高浓度食醋的生产工艺进行了简述,对每一工序的工作都进行了要点说明.     

联结基团含羟基的季铵盐Gemini表面活性剂的合成及胶团化行为研究

合成了一种联结基团为含羟基亚甲基链的季铵盐Gemini表面活性剂,即C12-3(OH)-C12.2Cl,用红外光谱、核磁共振及元素分析对它们的结构进行了鉴定,并对影响反应的因素进行了讨论,得出了合成C12-3(OH)-C12.2Cl的最佳条件为十二叔胺:十二叔胺盐酸盐:环氧氯丙烷摩尔比为2.0∶1.0∶1.0,以正丙醇为溶剂,在回流温度下反应3 h,产率可达94.5%以上;采用表面张力法、瞬态荧光法研究了C12-3(OH)-C12.2Cl在水溶液中的胶团化行为,发现C12-3(OH)-C12.2Cl的胶团生成能力远比其单体强,cmc值降低一个数量级,胶团聚集数随表面活性剂浓度增大而增大。     

优化营养方式强化蛋白核小球藻生物量及蛋白质和叶绿素生产

本文通过优化营养方式和培养条件,提高了蛋白核小球藻生物量及细胞内蛋白质和叶绿素含量。结果表明,葡萄糖浓度能显著影响蛋白核小球藻混养和异养生长的生物量浓度(p0.05),但不同硝酸钠浓度影响不显著。在葡萄糖浓度50 g/L、硝酸钠浓度3.75 g/L条件下,小球藻异养培养4 d,即可达到最高生物量浓度为21.31 g/L,显著高于盐度15‰条件下混养所得最高生物量浓度(14.32 g/L)(p0.05)。当葡萄糖耗尽,将小球藻细胞经含氮且不含糖的培养基适当稀释后进行光诱导培养,并优化硝酸钠浓度。发现在高异养细胞密度(11.09 g/L)下,采用硝酸钠浓度(3.75 g/L)和低光强(6,411±532 Lux)诱导培养藻细胞48 h,即可获得高蛋白质含量(54.10%)和高叶绿素含量(3.14%)的小球藻,相对于光诱导培养前,分别提高了207.74%和342.25%,蛋白质和叶绿素产率也显著高于单独混养或异养培养的最高值,分别达到1.32 g/(L·d)和0.09 g/(L·d)。     

PCR-DGGE分析东北自然发酵酸菜中的微生物多样性

为了探明传统的自然发酵酸菜中微生物的多样性和优势菌群,通过聚合酶链式反应–变性梯度凝胶电泳(polymerase chain reaction-denaturing gradient gel electrophoresis,PCR-DGGE)技术分析酸菜发酵过程中微生物群落动态变化。结果表明:东北自然发酵酸菜中的细菌种类比较丰富,真菌在酸菜中存在相对较少。东北自然发酵酸菜在发酵早期的活跃菌为明串珠菌(Leuconostoc sp.),而后是发酵产酸的嗜酸乳杆菌(L.acidophilus)、发酵乳杆菌(L.fermentum)和植物乳杆菌(L.plantarum),最后是由植物乳杆菌完成发酵过程。其中明串菌株为酸菜发酵前期优势细菌,植物乳杆菌为发酵中后期优势细菌,东北自然发酵酸菜发酵过程中主要真菌为汉逊德巴利酵母(Debaryomyces hansenii)、热带假丝酵母(Candida tropicalis)、扩展青霉(Penicillium expansum),真菌数量随发酵时间的增加而减少,且种类也随时间的变化而不断变化。     

红甜菜萃取液蒸发浓缩过程研究(I)红甜菜萃取液蒸发浓缩动力学

对红甜菜萃取液的蒸发浓缩动力学作了研究。表明甜菜红色素损失速率为表观二级反应,温度的影响遵循Arrhenius方程,建立了甜菜红色素降解速率与料液温度、料液相对密度、抗坏血酸浓度相关联的蒸发浓缩动力学模型。新型异形竖板降膜蒸发器中蒸发浓缩过程中甜菜红色素吸光度实测值与动力学理论模型的吸光度预测值吻合良好,表明动力学模型对预测工业蒸发器浓缩过程中甜菜红色素损失程度具有良好的准确性;可用于指导工业生产。