AGAR AND GELATIN GEL FLAVOR RELEASE

The taste suppression and rupture properties of 0.8-2.0% w/w agar gel and 3.0-6.5% w/w gelatin gel were studied by sensory evaluation and objective measurement. Flavor compound concentrations were determined to equalize the intensity of aspartame sweetness (0.02% w/w for both agar and gelatin gels), sodium chloride saltiness (0.9% w/w for agar gel and 0.2% w/w for gelatin gel), and caffeine bitterness (0.08% w/w for agar gel and 0.07% w/w for gelatin gel) in 1% w/w agar gel and 4.5% w/w gelatin gel. The coefficient of taste intensity = (concentration of flavor compound in the aqueous solution of equiintense taste in gel)/(concentration of flavor compound in gel) was used to compare the difference in gel taste suppression. The coefficient of saltiness intensity of 3.0% w/w gelatin gel exceeded 1.0, and those of other gels were below 1.0. The suppressed variation of the coefficient of saltiness intensity in agar gel was significantly (P<0.01) smaller than that of bitterness depending on agar concentration. No significant differences (P>0.05) in taste suppression between gelatin gels containing the 3 flavor compounds due to changes in gelatin concentration were observed. Rupture energy, which is related to mastication and is a common scale for agar and gelatin gels, was used to evaluate changes in suppression of the coefficient of taste intensities of the 2 gels. The coefficient of bitterness intensity of agar gels was more significantly (P<0.01) suppressed than sweetness and saltiness intensities of gelatin gels. The coefficient of sweetness intensity of gelatin gels was suppressed significantly less than bitterness (P < 0.05) of gelatin gels and sweetness (P < 0.05) and bitterness (P < 0.01) of agar gels.     

MECHANICAL PROPERTIES OF TWO-PHASE DISPERSE AGAR/GELATIN MIXED GELS

Agar/gelatin mixed gels with the same composition but with a different two-phase disperse structure were prepared and their mechanical properties compared. The agar/gelatin mixture was first kept at temperature above the gelling temperature of gelatin but below that of agar and stirred for the selected period, before cooling it below the gelling temperature of gelatin. For the low rupture stress system the agar concentration was 0.7% (w/w), while the gelatin concentration was 4.5% (w/w) to achieve the same rupture stress as the agar gel. The mixing temperatures selected were 20 and 37C. For the high rupture stress system, the agar and gelatin concentration was 2.8 and 10.4% (w/w), respectively, to achieve the same rupture stress. The mixing temperatures selected were 37 and 40C. The both mixed gels prepared by this method consisted of a dispersed phase of agar and a continuous phase of gelatin. The rupture stress of the mixed gels decreased as the content of the dispersed phase increased. The rupture stress had a tendency to be lower as the size of the dispersed particles increased. These results suggest that the interface between the dispersed phase and the continuous phase plays an important role as Griffith's crack, with the rupture of mixed gels occurring from that place.     

EFFECTS OF DIMENSIONS OF AGAR AND GELATIN GELS ON PALATAL PRESSURE PATTERNS

Eating of agar and gelatin gels in the mouth was studied dynamically in detail. The palatal presures on agar and gelatin gels of various concentrations and dimensions were detected by pressure transducers installed at three locations of the palate. For each of the gels, Pm (the maximum palatal pressure at the initial stage of mastication), P (the mean palatal pressure), W (work), and T (retaining time in the mouth) changed significantly when their concentrations increased. Moreover, gel dimensions also affected Pm, P and W. For a bite-size gel, Pm, P and W increased or remained constant, while for a finer sized gel, Pm, P and W were nearly constant regardless of the increase in rupture strength or gel concentration.     

COMPARATIVE ANALYSIS OF TRYPAN BLUE AGAR AND CONGO RED AGAR FOR THE ENUMERATION OF YEAST AND MOLD USING THE HGMF SYSTEM1

Enumeration of yeast and molds from 39 food samples, including 6 dairy products, 2 meat products, 5 cereal products, 9 fruits, 4 vegetables, 6 beverages, 4 spices, and 3 condiments on Trypan blue (at 1: 10,000 dilution) in potato dextrose agar (Trypan blue agar) was compared with Congo red (at 25:1,000,000 dilution) in potato dextrose agar (Congo red agar) using the hydrophobic grid-membrane filter (HGMF) technique of the ISO-GRID system. Yeast and mold grew well on both Trypan blue agar and Congo red agar, producing blue and red colonies, respectively, in the ISO-GRID system, when examined in incan-descent light. However, not all yeast and mold colonies grown on Congo red agar fluoresced under ultraviolet (UV) light (a recommended observation procedure). Thus, results indicated that Trypan blue agar observed in incandescent light is more convenient to use for enumerating yeast and mold in food samples.     

RHEOLOGICAL PROPERTIES OF MIXED GELS

The rheological properties of carrageenan/gelatin and agar/gelatin mixed gels were investigated by measuring the rupture properties, the texture parameters and the dynamic viscoelasticities. fie melting point, transparency and syneresis of these gels were measured in order to obtain the relationship with the rheological properties. The physical properties of the two mixed gels were slightly different. The agar/gelatin mixed gels generally showed the hindered effect of gelatin. The brittleness of agar gel disappeared on mixing with gelatin. It then became a flexible, cohesive and transparent gel. Carrageenan/gelatin mixed gels showed a decrease in the values of almost all of the mechanical properties when compared with carrageenan gels. However, the rupture properties of the C0.5 mixed gel were much higher than those of simple carrageenan gels.     

EFFECTS OF PHYSICAL PROPERTIES AND ORAL PERCEPTION ON TRANSIT SPEED AND PASSING TIME OF SEMILIQUID FOODS FROM THE MID-PHARYNX TO THE HYPOPHARYNX

The results of two sensory analyses, using healthy young individuals as assessors and semiliquid foods with markedly different physical properties as samples, were compared. One analysis required the assessors to perceive the food texture by oral perception alone and to use it as a basis for predicting the ease of swallowing of the bolus samples (i. e., the mobility of the samples through the pharynx) without actually swallowing the samples. The other analysis required the assessors to evaluate the mobility of the bolus samples through the pharynx, by actually swallowing them. Comparison of the results implied that human beings predict how easy it is to swallow a bolus (i. e., the mobility of the bolus through the pharynx) by perceiving in the oral cavity the texture of the food. Examinations were also made on the relationship between the evaluation of mobility of the bolus through the pharynx obtained by sensory analyses, and the transit speed and passing time of the bolus samples obtained by videomanofluorography. It was recognized that the front end speed was fast for semiliquid food samples that were soft and easy to swallow (and therefore easy to move through the pharynx), whereas the front end speed was slow for semiliquid food samples that were hard and difficult to swallow (and therefore perceived as being difficult to move through the pharynx.) These findings suggest that human beings' perception of the ease of swallowing of semiliquid food is closely related to the front end speed of the bolus. No significant difference was found among samples, either in the tail end speed of the bolus samples, or in the passing time from the front end to the tail end of the bolus samples. These results imply that, through some kind of swallowing efforts, healthy individuals are controlling the passing time through the pharynx of boluses with markedly diflerent physical properties, so that the time remains constant.     

Texture Profile Analysis and Functional Properties of Gelatin from the Skin of Three Species of Fresh Water Fish

The texture profile analysis and functional properties of gelatin from fresh water fish (carps) and porcine skin were measured. Texture profile analysis revealed that the porcine gelatin showed significantly higher values for hardness, springiness, cohesiveness, gumminess, and chewiness than carp skin gelatin (p < 0.05). The bloom strength of gelatin from a porcine source was higher (466.40 g) than carp skin. The solubility profile of gelatin from carps and porcine as function of sodium chloride concentration indicated a maximum solubility at 0.3 M. The relationship between emulsion capacity values and concentration of proteins were found to be inversed in all of the gelatin samples.     

兔皮明胶功能特性及其影响因素

为研究兔皮明胶的功能特性,对兔皮明胶的流体特性、全质构特性等进行测定。结果表明兔皮明胶对剪切速率的敏感性较小,其硬度、胶着性、咀嚼性和弹性高于猪皮明胶,在耐咀嚼的糖果类食品、肉制品生产中具有应用优势。色差检测结果表明兔皮明胶对产品的外观颜色影响较小,在实际应用中可替代猪皮明胶。不同质量浓度和pH值条件下,兔皮明胶和猪皮明胶加工特性的测定结果表明,兔皮明胶的黏度、起泡性总体均高于猪皮明胶;兔皮明胶的黏度随质量浓度的增加而增大,当质量浓度为4 g/100 mL时达到最大,当pH值靠近等电点时,其黏度减小;兔皮明胶的起泡性随质量浓度增加呈上升趋势,在质量浓度为3 g/100 mL时达到最佳。兔皮明胶的乳化稳定性随质量浓度和pH值的增大呈现先升高后降低的趋势,当质量浓度和pH值分别为3 g/100 mL和4.0时乳化稳定性达到最佳,且均高于猪皮明胶。     

响应曲面法优化苜蓿成冻特性研究

采用响应曲面法(RSM)研究了明胶、魔芋胶和蔗糖酯用量对苜蓿成冻特性的影响。建立苜蓿成冻的二次多项数学模型,并验证模型的有效性,得出优化的工艺条件为：明胶用量3.00%,魔芋胶用量3.00%,蔗糖酯用量2.93%,在此条件下,苜蓿冻的硬度为4477g,黏着性为－ 6456g,内聚性为0.3127,胶着性为1408g,咀嚼性为1388g。     

Release of active compounds from agar and agar–gelatin films with green tea extract

Active biodegradable films based on agar and agar–fish gelatin were developed by the incorporation of green tea aqueous extract to the film forming solution. The effect of the partial replacement of agar by fish skin gelatin as well as the addition of the green tea extract on the physical properties of the resultant films was evaluated. Special attention was given to the release of antioxidant and antimicrobial compounds from the agar film matrices with and without gelatin. Agar–gelatin films were less resistant and more deformable than agar films. The inclusion of green tea extract decreased tensile strength and elongation at break in both agar and agar–gelatin films. Water vapour permeability and water resistance was not affected either by the replacement of agar by gelatin or the addition of green tea extract, but the water solubility noticeably increased in the films containing green tea extract. The presence of gelatin in the agar–green tea matrix film hindered the release of total phenolic compounds, catechins and flavonols in water. As a consequence, the antioxidant power released by the films was lower in the case of films containing gelatin. However, the antimicrobial activity of the films was not affected by the presence of gelatin.     

PALATAL PRESSURE PATTERNS OF GELATIN GELS IN THE MOUTH

Palatal pressures of gelatin gel at various concentrations were detected by pressure transducers set at three locations in the palate. The following parameters were derived from the palatal pressure patterns: P, mean of palatal pressure from the beginning of eating to the end of swallowing; S, the last pulse of swallowing; T, retaining time of the sample in the mouth and W, energy consumed in the course of time until swallowing. P and W increased as the gelatin concentration increased from 1.0–4.0% and then they decreased as the gelatin concentrations exceeded 4.0%. T increased linearly over the whole range of gelatin concentrations. Changes in gelatin concentration had little effect on S. It was concluded that oral action changed primarily from crushing by the tongue against the palate to biting by the teeth as the toughness of the gelatin gel increased.     

Rheological properties of gelatin from silver carp skin compared to commercially available gelatins from different sources

Gelatin is used as a functional ingredient in many foods, pharmaceuticals, and cosmetics as a stabilizing, thickening, and gelling agent. The rheological properties of gelatins are important in the potential functionality of gelatin. This study is designed to determine the rheological properties of gelatin extracted from the skins of silver carp (Hypophthalmichthys molitrix Valenciennes 1844). The extracted gelatin is compared with commercially available gelatins from different sources. The results indicate that the stress-strain relationship of gelatin gels remained in the linear region over a broad range of strains and stresses and gave similar elastic moduli at varying frequency, stress, and strain levels. One exception was a commercial high molecular weight fish skin gelatin that gave a lower elastic modulus indicating that its gel strength was low compared to the other gelatin samples studied. Gel strength varied between 220 and 1230 g while viscosity varied between 4.53 and 6.91 cP among the samples. Melting and gelling temperatures varied between 14.2 and 32.3 °C and 3.2 and 25.4 °C, respectively. Texture profile analysis was done at 2 deformation levels, 25% and 75%, and the results correlated well with gel strength. The correlations between hardness, cohesiveness, and gumminess and gel strength were 0.98, 0.82, and 0.99, respectively, at 25% deformation but lower at 75% deformation. The results suggest that rheological measurements might be used to quickly estimate gel strength using less material. In addition, the silver carp skin gelatin seemed to be of equal quality to some of the commercial gelatins.     

SIMULTANEOUS RECOVERY AND DETECTION OF FOUR HEAT-INJURED FOODBORNE PATHOGENS IN GROUND BEEF AND MILK BY A FOUR-COMPARTMENT THIN AGAR LAYER PLATE

A four‐compartment thin agar layer (4‐TAL) system was developed to improve operation efficiency and recover injured foodborne pathogens simultaneously. The system consisted of a layer of nonselective agar overlaid on four different selective agars (xylose lysine desoxycholate [XLD], cefsulodin irgasan novobiocin [CIN], modified Oxford medium [MOX] and MacConkey sorbitol agar [MSA]) housed in a four‐compartment petri dish. We applied this system to simultaneously recover heat‐injured (55C, 10 min) Escherichia coli O157:H7 (MSA), Listeria monocytogenes (MOX), Salmonella Typhimurium (XLD) and Yersinia enterocolitica (CIN) from ground beef and pasteurized milk. No significant difference (P > 0.05) occurred between the single recovery unit (nonselective agar overlaid on one selective agar in a standard petri dish) and the 4‐TAL for detecting four heat‐injured pathogens in tested samples. Both TAL methods showed greater recovery of four heat‐injured pathogens than the pathogen‐specific selective media (P < 0.05). The 4‐TAL system appears to be efficient for recovery and detection of injured pathogens in food in terms of operation, material and labor costs, and space of incubation.     

BACTERIOLOGICAL ANALYSES OF FROZEN SHRIMP. 2. Staphylococci in Precooked Frozen Chilean Shrimp

SUMMARY– 392 samples of precooked frozen shrimp from two Chilean manufacturers, A and B, were quantitatively examined for the presence of Staphylococcus aureus by direct plating on Difco mannitol salt agar (MSA, 10% NaCI). 140 samples (35.7%) were found to contain Staphylococci but only half of these had counts of over 100,82.4% remaining within the acceptable limit. Frozen shrimps are prone to contamination by Staphylococcus during processing, especially if hand-processed, but these results show that it is possible to obtain a good-quality product when stringent sanitary measures are observed. MSA was compared with Baird Parker's egg yolk medium (BPM) by plating simultaneously on it 141 samples from manufacturer B; BPM detected S. aureus in a smaller number of samples (7.8%), and gave rise to fewer colonies than MSA. BPM seemed to be inhibitory even to some Staphylococcus strains, i.e., it is unsuitable for use in these frozen foods. From 2 other manufacturers, C and D, 80 samples of frozen shrimp, together with 60 nasal swab samples from food handlers were plated to investigate some cultural characteristics of S. aureus. 57 strains of this organism were obtained, 41 belonging to shrimp samples and 16 to nasal carriers from both manufacturers. The strains were isolated and, when tested by anaerobic fermentation of mannitol, deep growth in cysteine agar, catalase and coagulase reactions, all gave positive tests. Phosphatase and DNase reactions were less constant. All the strains with 1 exception were sensitive to 8 antibiotics tested. Thus, the general properties ascribed to S. aureus species appear unaltered in frozen shrimps. 28 strains (49.1%) could be typified with the set of 21 international phages, most of them belonging to group III; only in manufacturer D strains coming from food and food handlers were phage type related. In manufacturer C most strains were untypable.     

Microwave Heating of Agar Gels Containing Sucrose

A mathematical model was developed for predicting the temperature profiles of cylindrical samples of sucrose containing agar gels heated by microwaves. Temperature was modeled in terms of dielectric properties of gels and the power absorbed by the sample. Experimental corroboration of the predicted temperatures was obtained by microwave heating cylindrical gels of 2% agar containing 0, 40, and 60% sucrose. The levels of sucrose in the gels notably affected the temperature profiles in the cylinders. Samples with no sucrose showed a pronounced central heating effect, 40% sucrose samples showed a early uniform heating profile and 60% sucrose samples showed surface heating.     

基于低场核磁共振技术的注胶肉快速检测

目的:探索并建立一种新的注胶猪肉快速检测方法.方法:以正常猪肉及注射不同种类胶(黄原胶、卡拉胶、明胶、琼脂)的注胶肉为对象,利用低场核磁共振并结合主成分分析法分析处理的检测数据,根据肉品中的水分存在状态及分布结果,对猪肉进行快速检测.结果:正常肉与注胶肉之间、各类注胶肉及不同注胶量之间在主成分得分图上具有很好的区分效果.结论:低场核磁共振技术结合主成分分析法可以快速区分正常肉与注胶肉.     

EFFECTS OF OIL DROPLETS ON PHYSICAL AND SENSORY PROPERTIES OF O/W EMULSION AGAR GEL

Effects of oil droplets in an agar gel matrix were investigated by mechanical analyses and sensory evaluation. The results for compressive and puncture properties were expressed in terms of relative values. All compressive properties; stress, strain and compressive energy of emulsion gels, as obtained by compression tests, decreased with both increases of oil droplet size and oil volume fraction. The stress, strain and energy of the emulsion gels obtained by puncture tests did not change with an increase in oil droplet size. Results of sensory evaluation showed that the sample containing small oil droplets was harder than that with large oil droplets. On the other hand, the large oil droplet sample was oilier than that with small oil droplets. The sensory evaluations for hardness and oiliness of emulsion gels did not exhibit significant relations to most of the properties of mechanical analyses.     

Development of low‐fat sausages using basil seed gum (Ocimum bacilicum L.) and gelatin as a fat replacer

This research was performed to evaluate the rheological properties of myofibrillar protein gels (MPs) with basil seed gum (BSG) alone or in combination with gelatin (0.25%, 0.5%), and to determine the physicochemical properties of low‐fat sausages (LFSs) manufactured with BSG alone (0.5%) or combined with gelatin (0.25%). Viscosity and cooking yields (%) of MPs with BSG alone or in combination with gelatin were higher than those of the control. However, gel strength of MPs with the combination of BSG and gelatin (0.25%) was higher than that with BSG alone. The combination of BSG and gelatin produced a more stable and denser structure than control or BSG alone. In the LFSs, the addition of BSG reduced the percentages of expressible moisture and cooking loss, and the combination of the BSG and gelatin improved gumminess and cohesiveness compared to BSG alone. The use of BSG as a water binding agent and gelatin to improve gel formation will be considered as fat replacer for the manufacture of low‐fat comminuted sausages.     

DETERMINATION OF THE EFFECTIVENESS OF NOVOBIOCIN ADDED TO TWO AGAR PLATING MEDIA FOR THE ISOLATION OF SALMONELLA FROM FRESH MEAT PRODUCTS

Five plating media, Hektoen enteric (HE) and xylose lysine deoxycholate (XLD) agars with and without 80 and 5 μg/ml of novobiocin (N), respectively, and brilliant greeen sulfadiazine (BGS) agar with 80 μg/ml of the antimicrobial agent, were analyzed for the recovery of salmonellae from various fresh beef, pork, and poultry meat products. Of the total Samonella positive samples, 50.0% and 82.5% were found on XLD and XLD-N agars, respectively, 75.0% and 85.0% on HE and HE-N agars, respectively and 65.0% on BGS agar. HE-N and BGS media isolated three times more false positives than did XLD-N agar, while XLD and HE agars gave the highest numbers of false positives. The major H₂S producing false positive on XLD and HE agars was Proteus mirabilis. With the addition of N, P. mirabilis was eliminated, and the major H₂S producing false positive was almost exclusively Citrobacter freundii. The false positives on BGS agar were predominately distributed among C. freundii, Enterobacter sp., and Klebsiella sp.     

Effects of concentration on nanostructural images and physical properties of gelatin from channel catfish skins

Physical properties are crucial to gelatin utilization and the physical properties are determined by structure. Therefore, it is important to investigate the nanostructure and physical properties of gelatin over the full range of concentrations which are widely applied in research and industry. Nanostructure of gelatin can be investigated by atomic force microscopy (AFM). However, it is hard to obtain reliable AFM images of gelatin with high concentrations (1–6.67%). In this study, methods for imaging gelatin with high concentration were explored and developed, which mainly included six steps. Then the relationships among concentration, nanostructure and physical property of gelatin extracted from channel catfish skins (Ictalurus punctatus) were studied. The high-resolution AFM images show fibril structure in gelatins with concentrations from 1% to 6.67%. However, in low concentrations (<1%), most nanostructures of gelatin were spherical aggregates and fibril structure only existed occasionally. Correspondingly, there were no significant differences of gel strength, texture profile and viscosity among several groups of gelatin when the concentration was lower than 1%, in contrast, these properties changed dramatically when the concentration was greater than 1%. It indicates that there must be some close relationships among concentration, nanostructure and physical property of gelatin. The illustration of nanoscale transition would help us understand the macroscale changes of physical properties.