食品脆性和酥性的物理特征

 本文综述了食品主要织构性质脆性和酥性的力学、声学及组织结构特征,介绍了水分等因素对食品脆酥性的影响.     

不同嫁接组合对西瓜植株生长及果实品质的影响

采用优质中大果型西瓜品种中科1号为接穗,常规一段嫁接用抗生王、超丰F1、西嫁强生、京欣砧3号、野生西瓜1号、野生西瓜2号为砧木,二段嫁接采用西嫁强生作基砧、超丰F1作中间砧,研究了常规一段嫁接法与二段嫁接法对西瓜生长发育及果实品质的影响。结果表明,采用二段嫁接的西瓜植株生长势、抗枯萎病能力、单果质量、小区产量、中心可溶性固形物含量、瓜瓤果胶含量在所有嫁接组合中表现最佳,果实脆度与对照差异不显著。南瓜类砧木西嫁强生、京欣砧3号在生产上可大量推广,同时二段嫁接法具有一定的推广价值。     

辐照处理对新鲜藕带的影响

以新鲜藕带为试材,通过辐照冷杀菌的方法对其进行处理。研究结果表明,辐照剂量在6kGy时,微生物达标,随着辐照剂量的增大,其褐变度加深,脆度变小。     

Cracks in bread crust cause longer crispness retention

Crispness is among the most important factors that the consumer uses to assess the quality of crispy bread. However, this quality attribute is rapidly lost after baking. It is known that crispness retention can be increased more than eight times by enhancing the water vapor permeability of the crust. Current methods to achieve this, i.e., puncturing the bread before baking, require an extra process step. We hypothesize that cracks that appear spontaneously on the crust surface after baking can also enhance water vapor permeability and therefore improve crispness retention. We were able to confirm this hypothesis by preparing composite breads containing the same crumb but different crusts, with crust recipes of varying starch/protein ratios. Crusts systems that were generally high in gelatinized starch content and poor in evenly distributed gluten were more prone to crack after the whole process of part-baking, freezing, and baking off. These cracks led to an increased water vapor permeability of the crust and an eight times longer instrumental crispness retention compared to standard bread. In this paper we also discuss possible causes for crack formation in the crust. We hypothesize that effective cracks are caused by thermal shock in materials with a low ability to dissipate energy.     

Does crumb morphology affect water migration and crispness retention in crispy breads?

Crispness of bread is rapidly lost because of water migration inside the crumb towards the crust. How crumb properties determine this process independent of crust properties has not been examined before. Therefore, the aim of this study was to analyze and explain the influence of crumb morphology on the overall crispness retention. Crispness retention was determined by analyzing the acoustic emission of breads differing in either crust or crumb morphology. When crumb morphology is coarse with a lower number of large connections between the air cells, the effective diffusion coefficient is reduced. This effective diffusion coefficient of crumb, which equals approximately half the value of air, was estimated using X-ray micro-computer tomography images of crumb pieces. If the crumb has a lower effective diffusion coefficient, bread with similar crust properties has significantly longer crispness retention. Despite this, our data show that variations in properties of crust, which has 30 times higher permeability than crumb, have a larger impact on crispness retention than variations in properties of crumb.     

鳕鱼鱼皮水发工艺及机理研究

[目的]为优化鳕鱼皮水发生产工艺,并尝试对水发机理进行一些理论解释。[方法]以鳕鱼皮为试验原料,以水发率和蛋白损失率为指标,考察浸泡时间、NaOH溶液浓度、浸泡温度对鱼皮水发率的影响,通过正交试验对浸泡工艺进行优化,并考察了漂烫和冷激因素对产品爽脆度的影响。[结果]单因素试验结果显示,试验研究范围内,鳕鱼皮的水发率随NaOH溶液浓度的增大、浸泡时间的延长和浸泡温度的升高而先升高后下降。正交试验结果表明,鳕鱼皮在浓度为0.75 g/L的NaOH溶液中,在25℃条件下浸泡2.5 h时,鱼皮的水发率最好。并且通过80℃水浴,然后冰水浸泡3 min后得到的鱼皮具有较好的爽脆度。[结论]该研究为鳕鱼皮的综合利用提供了参考依据。     

Fracture behaviour of bread crust: Effect of ingredient modification

The influence of the formulation on the crispness of bread crust was studied. Crispness is a relevant sensory attribute that depends on several factors particularly the plasticizer content (water), the mechanical properties of the solid matrix and the morphological architecture of the bread. Enzymes and additives were used to modify the bread formulation. This resulted in a modification of the bread characteristics. Crust and crumb had higher porosity than the control breads and a decreased water content of the bread crust was found. Instrumental crispness was evaluated by simultaneous analysis of the fracture behaviour and sound emission while breaking the crust. Addition of lipase, amylase, glucose oxidase and hydroxypropyl methylcellulose (HPMC) increased the number of force and sound events, indicative of higher crispness. The number of fracture and sound events correlated negatively with the water content and positively with the porosity of the crust. Both properties are affected by the use of enzymes/additives. Whether the observed positive effect of the enzymes and additives on the number of force and sound events is due to a direct effect on the flour components properties or interactions or to an indirect effect via structure-water migration properties is still open to discussion.     

Assessment of apple (Malus × domestica Borkh.) fruit texture by a combined acoustic-mechanical profiling strategy

Texture of apple fruit originates from anatomic traits related to cell wall architecture and is one of its most important quality characteristics, thus there is the desire to better understand the different factors which contribute to apple texture. Here we present a novel approach based on the simultaneous profiling of the mechanical and acoustic response of the flesh tissue to compression, using a texture analyzer coupled with an acoustic device. The methodology was applied to a 86 different apple cultivars, measured after two months postharvest cold storage and characterised by 16 acoustic and mechanical parameters. Statistical treatment of the data with principal component analysis (PCA) allowed for the identification of three groups of variables, the mechanical ones being clearly distinguished from the acoustic ones. Moreover, the distribution of the apple cultivars in the multivariate PCA plot allowed characterisation of the cultivars according to their textural performance. Each cultivar was analyzed also with non-destructive vis/NIR spectroscopy in order to determine impartially the ripening stage. Sensory evaluation by panellists was performed on a selected group of cultivars and sensory data correlated with the acoustic-mechanical data. The results demonstrate the good performance of our combined acoustic-mechanical strategy in measuring apple crispness as it is perceived by human senses.     

Permeability of crust is key to crispness retention

Bread loses crispness rapidly after baking because water originating from the wet crumb accumulates in the dry crust. This water accumulation might be increased by the dense and low permeable character of the bread crust. Our objective was to investigate the influence of permeability of the crust on water uptake in the crust and on crispness retention. To achieve this objective, we increased the permeability of the control bread crust by creating small channels through the crust. The water vapour permeability of the crust with and without channels was measured using a newly developed method for brittle materials. Two further properties were measured over time: crispness of bread by analysing acoustic properties and water content of the crust. Control bread crust had low water vapour permeability and functioned as a barrier, leading to increased uptake of water in the crust. Water uptake was halved, however, if the water vapour permeability of the crust was doubled. As a consequence, crispness retention increased eight-fold; breads stored for four hours were as crispy as control breads stored for 30 min. We can conclude, therefore, that permeability of crust is key to crispness retention.     

The role of the gluten network in the crispness of bread crust

Crispness features of baked products strongly determine consumer acceptability. For many baked products, such as bread, the outer crust gives the crispy sensation. Confocal scanning laser microscopy of the structure of bread crust revealed a continuous protein phase and a discontinuous non-gelatinized starch phase in the outer crust. In contrast, the crumb and inner crust, showed a gelatinized starch network associated with a protein network. The role of the protein phase of the outer crust in determining crispness has been studied. During storage, the crispness of bread crust alters as a result of changes in water content/activity resulting from moisture redistribution within the bread and between the bread and its environment. Water content was affected by the flour protein content and by selectively modifying the crust protein phase of a model bread with enzymes, as well as by storing breads at high and low relative humidity (80–40% RH). Protease modification resulted in a lower water content and activity in the crust during the first hours of storage. In contrast, modification by transglutaminase had the opposite effect and gave rise to higher water retention of the crust compared to the un-treated d bread. This shows that modification of the protein network can be used to regulate the water holding capacity of the crust. Sensory analysis confirmed the retention of crispness in protease modified bread crust after 2 h storage at 80% RH conditions, whereas both the untreated and transglutaminase-treated breads lost their crispness. A negative relationship between water activity/content and crispness was found. Modification of the starch phase of the crust by alpha-amylase produced a bread crust with a low water activity. However, a steep increase in the water activity was observed after 2 h storage at 80% RH with a concomitant loss of crispness. These results indicate an important role of the gluten network in determining crust properties.