STARCH MOBILIZATION AND SUCROSE ACCUMULATION IN THE PULP OF KEITT MANGOES DURING POSTHARVEST RIPENING

Sugar is a determinant for the quality of mangoes, but information about its accumulation is scarce. Although starch can contribute to sugar production during ripening, not much is known about the enzymes involved. This work presents the changes in carbohydrate and enzymes during the development and ripening of Keitt mangoes. Starch disappearance was concomitant to a fivefold increase of sucrose, the most abundant sugar of the ripe fruits. The activities of α-amylase, β-amylase, phosphorylase and isoamylase were detected in the pulp, and while α-amylase increased parallel to the starch content, β-amylase presented a 20-fold increase during ripening. On the other hand, high phosphorylase activity was observed when fruits were still accumulating starch, and lowered during ripening. Isoamylase was detected during development and increased slightly during ripening, which would be in agreement to the expected role for isoamylases as acting on both subproduct of starch synthesis and degradation.

PRACTICAL APPLICATIONS

The present work reinforces our previous works that Keitt mangoes do not ripen when attached to the tree. This fact allowed us to study all the starch degradation after mango harvesting which does not occur with the other cultivars. Data obtained in this work reinforce the role of α-amylase, β-amylase and isoamylase rather than the starch phosphorylases on starch granule degradation in mangoes, and the subsequent soluble sugar accumulation.     

复合酶制剂对甜酒酿面包发酵烘焙特性的影响

选用中国特色传统甜酒曲制作的甜酒酿进行面包制作,通过面团流变学分析、生物化学分析、激光共聚焦 显微观察、感官评定等多种手段对甜酒酿面团及面包的品质进行综合评估,与普通小麦面包进行对比,并使用天然 酶制剂来提高含甜酒酿面包的发酵烘焙特性。结果表明：含甜酒酿面团游离巯基含量增加,蛋白酶活力较强,甜酒 酿对面包面团面筋网络结构的形成有破坏作用,会导致面包内聚性、弹性下降,降低口感评分。但甜酒酿能给面包 带来更加诱人的色泽,其特有的酒香使面包更加可口,通过酶制剂的作用,面团面筋网络结构得到强化,含酶甜酒 酿面包品质全面提升,比普通小麦面包更受欢迎。     

传统酸面团中植物乳杆菌发酵馒头抗氧化特性及挥发性风味物质特征

以普通小麦馒头（记为WS）和植物乳杆菌标准菌株发酵馒头（记为LPS）为对照,通过测定总酚含量和1,1-二苯基-2-三硝基苯肼（1,1-diphenyl-2-picrylhydrazyl,DPPH）自由基清除能力,同时采用固相微萃取-气相色谱-质谱联用技术,研究传统酸面团中植物乳杆菌植物亚种发酵馒头（记为ZLPS）的抗氧化特性及挥发性风味物质特征。结果表明：乳酸菌发酵,尤其是植物乳杆菌植物亚种的发酵可以明显改善蒸制带来的馒头抗氧化特性降低,与WS相比,ZLPS中总酚含量增加了108.70%,DPPH自由基清除能力为WS的13.65 倍;乳酸菌发酵酸面团使得馒头的挥发性风味物质含量增高,酸面团发酵馒头的挥发性风味物质总含量分别增加了53.11%（LPS）、56.92%（ZLPS）,且ZLPS还产生了一些独特的挥发性风味物质,如乙酸异戊酯、6-甲基-5-庚烯-2-酮、3-辛醇、2-乙基己醇、乙酸-2-苯乙基酯等;ZLPS各项指标评分均较高,更具有获得消费者青睐的潜力。     

SIMULTANEOUS HEAT and MASS TRANSFER DURING the DEEP FAT FRYING of TORTILLA CHIPS

The heating and water loss of a single tortilla chip during deep fat frying was investigated experimentally and the data were analyzed by writing two heat and mass transfer balances. the equations were solved using explicit finite difference technique. Oil uptake as a function of frying time was described by a first order exponential equation. the empirical and theoretical heat and mass transfer agreed well.
The effect of oil temperature on the moisture loss and oil uptake as a function of frying time was analyzed. Moisture loss rate increased as temperature increased. the effects of temperature on oil uptake were not significant during the first 15 s of frying, however, the final oil content was higher for the tortilla chip fried at 190C than at 150C for 60 s.     

DETERMINING TOPOLOGICAL CHANGES AND CRITICAL LOAD LEVELS OF A POWER SYSTEM BY MEANS OF ARTIFICIAL NEURAL NETWORKS

ABSTRACT

In this paper, an investigation is done of the possibilities of implementing multi-layered artificial neural networks in analyzing the dynamic stability of an power system during load and topology changes. To solve this problem, a multi-layered neural network is used whose inputs are the state vector components, and whose outputs are encoded line outages and the real component of dominant eigenvalues of the system state matrix of the power system. The neural network is trained through the error back-propagation method. The proposed methodology is tested on an power system with ten nodes and four generators. The obtained results indicate the attractiveness of “on-line” application possibilities of multi-layered neural networks in order to efficiently evaluate the stability of an power system during conditions of load and topology change.     

A survey of the physicochemical and microbiological quality of ultra‐heat‐treated whole milk in Brazil during their shelf life

The objective was to evaluate the quality of important brands of ultra‐heat‐treated (UHT) milk marketed in the northern of Parana State, Brazil, during the shelf life of the product. Five brands were analysed at 30, 60, 90 and 120 days after UHT milk production. The physicochemical quality of the milk was assessed in terms of fat content, titratable acidity, density, freezing point depression, total solids, solids‐not‐fat, proteolysis and alcohol stability. Microbiological quality was assessed by the enumeration of aerobic mesophilic micro‐organisms. None of the brands complied with all the physicochemical standards. Two brands met all applicable microbiological requirements. Gelation was observed from 90 days of storage onwards in all brands.     

USE of HYDROSTATIC PRESSIJRE to PRODUCE HIGH QUALITY and SAFE FRESH PORK SAUSAGE

The effects of high hydrostatic pressure (HHP) on the survival of microor ganisms and quality changes of fresh pork sausages were investigated. Pork sausage inoculated with Listeria monocytogenes at 1O⁷ CFU/gram was prepared and subjected to HHP at 414 and 552 MPa, at treatment temperatures of 25 and SOC. for various time intervals to examine pressure effects on inactivation of bacteria. At a pressure of 414 MPa and SOC for 2 min, the microorganisms in fresh pork sausages were completely inactivated. Partial discoloration of meat was observed after 10 min of pressurization above 414 MPa at either temperature.
The effect of HHP treatment on the physical and rheological properties of sausage was also studied. the sausages increased infirinness with an increase in the pressure applied. the pressure-treated sausages were generally lighter in color as compared with the heat-treated sausages.
The optimal pressure/temperature/time conditions that resulted in minimum quality changes with microbiologically safe fresh pork sausages was 414 MPa and SOC for 2 min.