Lightness and gloss of peach gels: effect of fruit and sugar content

 Lightness and gloss were studied in peach gels prepared with different quantities of sugar and peach pulp, using a mixture of xanthan and locust bean gum as gelling agents. Colour was described in terms of the colour coordinates established by the Commission Internationale de l'Eclairage and gloss was determined as a percentage. The values of lightness determined optically (L^*), when ranked, corresponded well with those determined by eye, but there was less similarity between the ranked values of gloss determined optically and by eye. There was a clear relationship between the sensory evaluation of lightness and gloss and the fruit and sugar content of these gels. Mathematical equations were developed to relate both L^* and gloss values determined optically with fruit and sugar concentrations. It was found that fruit had a greater effect than sugar on the L^* values and that gloss depended only on the sugar content. Finally, the gloss of gels prepared with different gelling agents were compared and it was found that lightness can affect the sensory evaluation of gloss. Received: 15 July 1997 / Revised version: 3 February 1998     

Enzymatic activities related to cherimoya fruit softening and sugar metabolism during short-term controlled-atmosphere treatments

 The effects of short controlled-atmosphere (CA) treatments, involving exposure to 10% O₂ combined with 10%, 15% and 20% CO₂, on a selection of biochemical parameters and related enzymatic activities of cherimoya fruit were studied. A marked increase in the activity of soluble and cell-wall invertases was found in cherimoyas stored in air, but this was inhibited by CA treatment, which also reduced the accumulation of soluble sugar and malic acid. CA had no effect on the citric acid content and enhanced the rise in fumaric acid concentration, which was directly related to the CO₂ level. Differences in the softening of fruit stored in air and in CA were found after 9 days of storage, but the role of the cell-wall hydrolases polygalacturonase and carboxymethyl-cellulase in this behaviour was not elucidated. Received: 25 January 1998 / Revised version: 3 March 1998     

Enzymatic activities related to cherimoya fruit softening and sugar metabolism during short-term controlled-atmosphere treatments

 The effects of short controlled-atmosphere (CA) treatments, involving exposure to 10% O₂ combined with 10%, 15% and 20% CO₂, on a selection of biochemical parameters and related enzymatic activities of cherimoya fruit were studied. A marked increase in the activity of soluble and cell-wall invertases was found in cherimoyas stored in air, but this was inhibited by CA treatment, which also reduced the accumulation of soluble sugar and malic acid. CA had no effect on the citric acid content and enhanced the rise in fumaric acid concentration, which was directly related to the CO₂ level. Differences in the softening of fruit stored in air and in CA were found after 9 days of storage, but the role of the cell-wall hydrolases polygalacturonase and carboxymethyl-cellulase in this behaviour was not elucidated. Received: 25 January 1998 / Revised version: 3 March 1998     

Morphology of starch in surimi gels

 The purpose of this work was to study the changes undergone by starch during heat-induced surimi gel preparation either with or without added egg white, and their effects on the structure of gels using light and scanning electron microscopy. Gels were made from SA-grade Alaska pollack (Theragra chalcogramma) surimi with: (1) salt (3%, w/w); (2) salt and waxy corn starch (3% and 5%, respectively w/w); or (3) salt, waxy corn starch and egg white (3%, 5% and 5%, respectively, w/w). Final moisture was adjusted to 73% or 83%. The gels were prepared by prior setting (40°C, 30 min, followed by 90°C, 30 min) or cooking (90°C, 30 min). The prepared gel was frozen and stored at –20°C (±1°C) until analysis. Samples were observed by light and scanning electron microscopy. The results show that the starch granules alter according to the processing conditions, with the predominance of crystalline or amorphous morphology depending upon the availability of heat and water. Large cavities formed in the protein gel matrix during setting can trap water; as a result, water availability is limited for starch to swell and gelatinize even in the high-moisture gel. Received: 13 March 1997     

Effects of sugar, protein and water content on wheat starch gelatinization due to microwave heating

 Understanding the interactions between sugar, starch, protein and water, which are the main components of a baked product, will advance the development of high quality, microwaveable products. This paper presents a mathematical model describing the quantitative relationships between water, sugar and protein on the gelatinization of wheat starch following 20 s of microwave heat as determined by differential scanning calorimetry. Addition of sugar decreased the degree of gelatinization of starch due to microwave heating significantly. Water and protein were not found to be as significant as sugar in delaying gelatinization. The effects of sugar and protein on the gelatinization of starch were pronounced in water-limited systems. The model could be used to describe systems containing 33–67% water, 0–33% sucrose and 0–5.8% protein, with a coefficient of determination of 0.91. Received: 29 June 1998     

Determination of the carotenoid content in selected vegetables and fruit by HPLC and photodiode array detection

 Epidemiological studies have shown inverse correlations between the consumption of vegetables and fruit rich in carotenoids and the incidence of cancer and cardiovascular diseases. A total of 22 species of vegetables (including potatoes) and 28 of fruit (including rhubarb) were analysed for their contents of carotenoids by reversed-phase high-performance liquid chromatography (RP-HPLC) and photodiode array detection. A total of 27 carotenoids (among them β-carotene, lutein and violaxanthin also as cis isomers) were identified and quantified. Lutein, β-carotene (trans and cis forms) and violaxanthin were the predominant carotenoids in all green vegetables. Yellow and yellow-red vegetables and fruit contained β-carotene, α-carotene, β-cryptoxanthin and α-cryptoxanthin. Antheraxanthin and neoxanthin were found in nearly all produce. Lycopene was the predominant carotene in tomatoes, papayas and grapefruit. Vegetables with more than 10 mg of total carotenoids per 100-g edible portion were kale (34.8), red paprika (30.4), parsley (25.7), spinach (17.3), lamb’s lettuce (16.0), carrots (15.9) and tomatoes (12.7). In the case of fruit, grapefruit (3.5), papayas (3.4) and nectarines (2.4) were pre-eminent with more than 2 mg of total carotenoids (except for phytoene, phytofluene and ζ-carotene) per 100 g. Received: 27 March 1996     

Butter colour affects sensory perception of spreadability

 Two butter samples of significantly different yellowness were subjected to cone penetration experiments to measure their apparent yield value, as an instrumental measure of spreadability, at different temperatures. A ten-member panel evaluated sensory spreadability of selected pairs of samples, adjusted to particular apparent yield values, by means of simple difference tests both in the daylight and in a dark-room under red light. The results imply that sensory perception of spreadability is heavily affected by butter colour. Whereas the results of the dark-room experiments were in line with instrumental measures, the more yellowish butter was selected as the “easier-to spread” sample when colour differences were perceptible by the panellists. Received: 26 November 1996     

Sweetness and texture perceptions in structured gelatin gels with embedded sugar rich domains

Layered and homogeneous gelatin gels with controlled rheological properties were compared for their sensory characteristics, specifically sweetness, hardness, breakdown behaviour and frothing. All gels and layers had a gelatin/water concentration of 5%. The total sugar concentration was 9% in the layered samples and 0, 9, 15 or 22.5% in the homogeneous samples. These concentrations corresponded to the concentrations in the single layers.A seven-layered sample with different sugar concentrations in the layers gave a higher early sweetness intensity than a homogeneous gel with the same mean total sugar concentration. All layered gels were similar in hardness, breakdown behaviour and frothing; for the homogenous samples, sensory hardness was decreased in samples with much sugar. These gels also fell into smaller pieces than the sugarless sample. This study shows that it is possible by controlling the sugar distribution within a sample to produce sweeter gels while the sugar content is maintained.     

Sweetness and texture perception in mixed pectin gels with 30% sugar and a designed rheology

Pure low-methoxyl (LM) pectin and mixtures of LM and high-methoxyl (HM) pectin in different ratios were used to produce gels with control over the rheological parameter storage modulus (G′). The gels either had similar pectin concentrations and different G′ values, or different pectin concentrations and similar G′ values. All gels were prepared with 30 g/100 g sugar, in the presence of 0.1 g/100 g CaCl₂, at pH 3.5; these are conditions that favour gel formation of both LM and HM pectin.The gels were compared for their sensory characteristics; specifically sweetness, sourness, thickness, and glueyness. Sweetness was found to increase with increasing storage modulus (G′) in pectin gels of similar pectin concentration, but different G′ values. Gels with higher proportions of LM pectin were perceived as sweeter than those with low LM pectin ratios. These gels also had increasing loss modulus (G″), and increasing differences between G′ and G″, which indicates that diffusion has a bearing on the perception of sweetness in pectin gels. Thickness and glueyness were mostly determined by total pectin concentration. Thickness also increased with increasing LM pectin concentration while glueyness increased with increasing HM pectin concentration.     

Colour of hard cheese 2. Factors of influence and relation to compositional parameters

 Colour properties of hard cheeses, which included mature Vorarlberger Bergk?se (n=141) as well as a set of Emmental cheeses monitored periodically during ripening, were evaluated by tristimulus reflectance measurements. After transformation of the tristimulus primaries into the recently proposed one-dimensional Yellowness index, colour measures were related to selected compositional parameters by multivariate statistical methods. Both multiple regression and principal component regression showed that cheese body colour is mainly affected by qualitative properties of the fat phase which, in turn, are heavily influenced by seasonal deviations. Additional minor sources of variation include the total solids content as well as measures reflecting changes induced by cheese maturation. Received: 15 July 1996     

Colour of hard cheese 2. Factors of influence and relation to compositional parameters

Colour properties of hard cheeses, which included mature Vorarlberger Bergkäse (n=141) as well as a set of Emmental cheeses monitored periodically during ripening, were evaluated by tristimulus reflectance measurements. After transformation of the tristimulus primaries into the recently proposed one-dimensional Yellowness index, colour measures were related to selected compositional parameters by multivariate statistical methods. Both multiple regression and principal component regression showed that cheese body colour is mainly affected by qualitative properties of the fat phase which, in turn, are heavily influenced by seasonal deviations. Additional minor sources of variation include the total solids content as well as measures reflecting changes induced by cheese maturation.     

Effect of protein concentration on whey protein gels obtained by a two-stage heating process

 The influence of protein concentration on the properties of gels obtained by a two-stage heating process was determined. In the first stage, whey protein dispersion (3–10%) was heated at pH 8.0, and in the second stage it was diluted to 3% protein, adjusted to pH 7.0 and heated again. Increased protein concentration in the first stage of polymerization resulted in the gels obtained in the second stage having a lower phase angle, increased storage modulus and increased hardness. Increased protein concentration also resulted in gels with an increased optical density, which suggests thathigher protein concentration leads to more and larger aggregates. Gels obtained from dispersions preheated at a higher protein concentration had higher permeability coefficient (B _gel) values. The increase in B _gel suggests that the higher protein concentration increased the size of the aggregates, which in a second stage of heating formed a gel matrix with a larger pore size. Received: 11 February 1999     

The effect of electrical processing on mass transfer in beetroot and model gels

The diffusion between solids and surrounding liquids has been studied under the influence of different electric field strengths varying between 0–1000 V m⁻¹, characteristic both of ohmic heating and Moderate Electric Field (MEF) processing. The rate of enhancement of mass transfer between slabs of beetroot and surrounding fluid has been studied at up to 60 °C, as a function of electric field strength and the orientation of the slab to the field. Enhancements in diffusion coefficient of up to a factor of 2 are seen, with decreased enhancement at higher temperature and when the electric field does not pass through the particle. Diffusion into gels has been studied and enhancement found only for alginate (an ionically set gel) and not for gelatin and egg albumin, that are thermally set gels.     

Firming of starch gels and amylopectin retrogradation as related to dextrin production by α-amylase

 The effect of dextrins produced by α-amylase on the firming and amylopectin retrogradation of wheat starch gels was studied. Different gel samples were prepared and included several ingredients, for example, α-amylase, vital gluten and glucoamylase. Amylopectin retrogradation, gel firming and the dextrin profile were analysed throughout a 5-day storage period. Both processes, i.e. firming and starch retrogradation, increased with time, and were not affected by the incorporation of gluten into the mixture. The well-known effect of α-amylase to retard bread crumb firming was also found to be relevant to starch gels. From the results obtained in this work, it seems that this anti-firming effect is not due to modifications of the starch but to dextrins produced by starch hydrolysis, since the effect did not occur when dextrins were removed by glucoamylase. Received: 30 December 1996     

Colour changes during manufacture of Galician chorizo sausage

 Galician chorizo sausage is a smoked-meat product containing chilli pepper. This study investigated changes in its colour (CIE colour coordinates L*, a* and b*, together with redness index, hue, chroma and perceived colour) during the curing process. Samples were obtained from three manufacturers (A, B and C) whose smoking and curing procedures differ markedly. Most of the colour measurement showed clear changes during curing. All measurement except external L* varied significantly among samples obtained from the different manufacturers. Pairwise comparisons indicated that in most cases there were significant differences between samples from manufacturer A (who smokes the product for only 6 h) and manufacturers B and C (who smoke the product for a longer period), but not between samples from manufacturers B and C. The pH, water activity and moisture content were also monitored; again, these variables differed significantly between A and B and between A and C, but not between B and C. Received: 8 October 1997 / Revised version: 19 January 1998     

Effect of gelatine on the texture of yoghurt and of acid-heat-induced milk gels

 A penetrometry study was made of the effect of the addition of gelatine on the texture characteristics of yoghurts and acid-heat-induced milk gels. Detailed analysis of the various penetration profiles provided valuable information about the nature of the samples studied. Gelatine was compatible with the milk systems over a wide range of concentrations and it prevented syneresis. In yoghurts prepared with and without the addition of skim-milk powder, the addition of increasing concentrations of gelatine up to 1.5% gradually modified the mechanical characteristics of the final gels. In acid-heat-induced milk gels, whose mechanical characteristics depend on the final pH value, the addition of increasing quantities of gelatine up to 6.67% practically eliminated this dependence, and the effect of pH was only significant in the gels with 1.5% gelatine, which were structurally weaker. Received: 3 June 1998     

Colour changes during manufacture of Galician chorizo sausage

 Galician chorizo sausage is a smoked-meat product containing chilli pepper. This study investigated changes in its colour (CIE colour coordinates L*, a* and b*, together with redness index, hue, chroma and perceived colour) during the curing process. Samples were obtained from three manufacturers (A, B and C) whose smoking and curing procedures differ markedly. Most of the colour measurement showed clear changes during curing. All measurement except external L* varied significantly among samples obtained from the different manufacturers. Pairwise comparisons indicated that in most cases there were significant differences between samples from manufacturer A (who smokes the product for only 6 h) and manufacturers B and C (who smoke the product for a longer period), but not between samples from manufacturers B and C. The pH, water activity and moisture content were also monitored; again, these variables differed significantly between A and B and between A and C, but not between B and C. Received: 8 October 1997 / Revised version: 19 January 1998     

Sensory quality of low-sugar orange gels with gellan, xanthan and locust bean gums

Effects of reducing the sucrose content (from 55 to 30 ^°Brix in the final product) and of the use of gellan gum or a mixture of gellan, xanthan and locust bean gums (3:1:1) on the mechanical characteristics (maximum rupture force and deformation at rupture) of orange gels prepared with 15% w/w fruit pulp, sucrose and different amounts of hydrocolloids (0.25, 0.4, 0.55 and 0.7% w/w) were studied by uniaxial compression. The concentration of aspartame needed to compensate for sweetness loss was determined by a paired-comparison constant-stimulus method. Sensory characteristics (texture, appearance and flavour) of low-sugar orange gels (30 ^°Brix) with 0.5% w/w aspartame and different amounts (0.55 and 0.7% w/w) of gellan or the mixture of gums were analysed by the free choice profile method in comparison with the high-sucrose reference material (55 ^°Brix and 0.4% w/w gellan). Use of the mixture of gums permitted the obtention of low-sugar orange gels showing mechanical characteristics similar to those of the reference gel, though some differences in texture were perceived. The low-sugar gels were slightly lighter in colour and slightly more bitter and refreshing than the reference sample. Received: 29 November 1995/Revised version: 13 May 1996     

Waxy corn starch affecting texture and ultrastructure of sardine surimi gels

 The effect of waxy corn starch (WCS) on the texture, water-holding capacity and microstructure of sardine (Sardina pilchardus) surimi gels in two different systems was studied. In the type A system, increasing amounts of WCS (2, 4, 6 or 8 g/100 g surimi) were added to surimi while maintaining the gel moisture constant at 78%; in the type B system, WCS was added without correcting the gel moisture. Gels were made using two different heat treatments [heat-induced setting (HS) and direct cooking (DC)]. When starch was replaced by surimi (type A) and a heat treatment was applied that favoured formation of a preliminary actomyosin (AM) network (i.e. HS), gel strength (GS) was lower than in the control and decreased as more starch was added, despite an increase in the amount of water held by the gel. Scanning electron microscopy (SEM) showed that the matrix network was fibrillar with a globular surface. Starch appeared to be totally gelatinized and surrounded by a continuous matrix. When the amount of dry matter in gels was increased (type B), in no case did starch have a reinforcing effect, despite an increasing water-holding capacity; SEM showed a denser continuous matrix surrounding the gelatinized starch. Both types of gel made using the heat treatment that allows simultaneous gelling of surimi and gelatinization of starch (i.e. DC) exhibited much poorer GS than did HS gels, while addition of starch made practically no difference to gel texture. The findings suggest that the effect of starch is related to the type of gel matrix that forms upon addition of ingredients. Although such gels contained more water or dry matter, their texture parameters were lower, possibly because of the type of network formed by sardine surimi. Nonetheless, gels of acceptable quality were successfully made with added starch by incorporating less surimi. Received: 18 March 1996     

Influence of processing on available carbohydrate content and antinutritional factors of chickpeas

 The effect of chickpea processing (soaking, soaking plus cooking and dry heating) on the content of available carbohydrate (monosaccharides, disaccharides and starch) and antinutritional factors (α-galactosides and trypsin inhibitor activity) was studied. Soaking produced a reduction in available carbohydrates (19–20%) and α-galactosides (16–27%), and either did not affect or caused a slight reduction of trypsin inhibitor activity (TIA) in chickpeas. Soaking plus cooking brought about a larger decrease in available carbohydrates (23–24%) and α-galactosides (45–58%), and completely eliminated TIA. Dry heating caused a 24% reduction in available carbohydrates, a 46% decrease in α-galactosides and a 27% decrease in TIA. Overall, cooking the presoaked seeds in water, acidic or basic solution seems to be adequate to obtain a chickpea flour with a large reduction in antinutritional factors (α-galactosides and TIA) and also a high level of available carbohydrate content. Received: 22 April 1999 / Revised version: 28 June 1999