Effect of toasting time on the browning of sliced bread

Slices of wheat bread were toasted for different times until a distinct intensity of brown colour was reached. Two assays were carried out: prolonged toasting times (5–60 min) and reduced toasting times (0.5–5 min). The browning indicators (furosine, available lysine, hydroxymethylfurfural (HMF), colour and absorbance at 284 and 420 nm) were determined. The precision of all indicators used was high (CV < 4%). No furosine or HMF was detected in the dough before baking. The furosine content increased until 7 min (299 mg per 100 g protein) and then decreased to 2.9 mg per 100 g protein at 60 minutes. For the first toasting times (0.5, 1 and 2 min) the furosine content decreased slightly. Available lysine reached losses of 50% after 25 min of heating. The toasting of bread increased HMF values from 12 to 2025 mg kg^?1 for the assay at prolonged times of heating and from 1.3 to 4.2 mg kg^?1 at reduced times (0.5–5 min). The HMF content decreased (1000 mg kg^?1) when the sliced bread was toasted until it burnt. Colour (ΔE, 100 ? L*) and absorbance at 284 and 420 nm always increased. High linear correlations (r² > 0.860) were obtained between browning indicators and time (A₂₈₄/time, A₄₂₀/time, 100 ? L*/time and HMF/time). © 2001 Society of Chemical Industry     

Indicators of non-enzymatic browning in the evaluation of heat damage of ingredient proteins used in manufactured infant formulas

Twelve infant formula ingredients of animal origin (caseinates, whey proteins and hydrolysates of casein and of whey proteins) and three of vegetable origin (soybean proteins) were analyzed. Furosine, hydroxymethylfurfural (HMF) and pyrraline were studied as indicators of thermal damage and available lysine as nutritional indicator, determined by HPLC in phase reverse and UV detector. The objectives were to evaluate heat damage to ingredients used in commercial infant formulas by measuring non-enzymatic browning indicators and to determine the nutritional value of these ingredients by available lysine determination. Very high furosine values were detected in whey proteins, ranging from 354 to 1,435 mg/100 g of protein. Lower furosine values were found in the remaining ingredients, ranging from 1.36 mg/100 g in hydrolyzed casein to 60.5 mg/100 g in sodium caseinate. Available lysine content ranged from 1.85 g/100 g of protein in hydrolyzed casein to 7.91 g/100 g in calcium caseinate. HMF was detected in whey protein samples between 0.16 and 2.47 mg/100 g of protein. Pyrraline was only detected in one sample of whey proteins at 41 mg/100 g of protein. Similar ingredients from different manufacturers show varied heat damage and nutritional values     

Available lysine and fluorescence in heated milk proteins/dextrinomaltose or lactose solutions

In order to predict and compare the effects of dextrinomaltose and lactose on available lysine loss by the Maillard reaction, six model systems were prepared by mixing casein, laboratory whey protein or commercial whey protein with dextrinomaltose or lactose. The solutions were prepared at concentrations similar to those used in enteral and infant formula processing and were heated at 100, 120 or 140 °C for 0–30 min. The progress of the Maillard reaction in these model systems was followed by monitoring free fluorescence intermediary compounds. Model systems with lactose showed higher available lysine less than the model systems with dextrinomaltose; linear lysine losses were obtained between 0 and 20 min at 100 and 120 °C. At sterilization temperature and time (120 °C/10 min), lysine losses of milk proteins with dextrinomaltose as reducing sugar were 6.1% for casein, 4.1% for laboratory whey protein and 13.4% for commercial whey protein. Available lysine showed correlation with furosine in model systems prepared with lactose and casein or laboratory but not commercial whey protein at 100 and 120 °C. The initial fluorescence value obtained by mixing casein or laboratory whey protein with lactose or dextrinomaltose was low (between 3.8 and 5.7), whereas the value obtained when commercial whey proteins were used was close to 9. At 120 °C/10 min, there was only a small increase of fluorescence in casein and laboratory whey protein but a large increase in commercial whey protein (threefold the initial value). Fluorescence measurement is useful for finding the extent of the Maillard reaction in commercial whey protein (thermally damaged protein). An absolute value greater than 10 may indicate that products were prepared with thermally damaged proteins.     

Studies on the impact of glycation on the denaturation of whey proteins

It could be shown for technologically relevant whey protein powders that denaturation of β-lactoglobulin (β-Lg) is affected significantly by the extent of covalent modification of lysine residues by lactose. The amount of acid soluble β-Lg as measured via RP-HPLC with UV detection after heating for 10 min at 80 °C increased from 40% (4.6% lysine modification) to 82% (22.4% lysine modification). An increase in glycation leads to a slower denaturation-induced oligomerisation, as shown by SDS-PAGE. Concomitant with an increase in lysine modification, the denaturation temperature increased from 79.5 to 84 °C, as measured by differential scanning calorimetry (DSC). Covalent attachment of lactose to whey proteins during preparation or storage significantly improves the heat stability of whey proteins, which may be of particular importance for the technological use of whey proteins varying in the degree of lysine modification.     

Impact of parboiling conditions on Maillard precursors and indicators in long-grain rice cultivars

The effect of steaming conditions (mild, intermediate and severe) during parboiling of five different long-grain rice cultivars (brown rice cultivars Puntal, Cocodrie, XL8 and Jacinto, and a red rice) on rice colour, and Maillard precursors and indicators was investigated. Rice colour increased with severity of parboiling conditions. Redness increased more than yellowness when parboiling brown rice. Parboiling turned red rice black. It changed the levels of glucose, fructose, sucrose, and maltose. Losses of the non-reducing sugar, sucrose were caused by both leaching into the soaking water and enzymic conversion, rather than by thermal degradation during steaming. Concentrations of the reducing sugars, glucose and fructose, in intermediately parboiled rice were higher than those of mildly parboiled rice. After severe parboiling, glucose levels were lower than those of intermediately parboiled rice, while fructose levels were higher. These changes were ascribed to the sum of losses in the Maillard reaction (MR), formations as a result of starch degradation and isomerisation of glucose into fructose. It was clear that the ε-amino group of protein-bound lysine was more affected by parboiling conditions and loss in MRs, than that of free lysine. Low values of the MR indicators furosine and free 5-hydroxymethyl-2-furaldehyde (HMF) in processed brown and red rices were related to mild parboiling, whereas high furosine and low free HMF levels were indicative of rices being subjected to intermediate processing conditions. High furosine and high free HMF contents corresponded to severe hydrothermal treatments. The strong correlation (r = 0.89) between the free HMF levels and the increase in redness of parboiled brown rices suggested that Maillard browning was reflected more in the red than in the yellow colour.     

Available lysine,protein digestibility and lactulose in commercial infant formulas

Available lysine, in vitro protein digestibility and lactulose values were determined in 23 commercial infant formulas. The mean available lysine content of the formulas based on dairy proteins was 66.7±9.5 mg g⁻¹ protein, similar to that of human milk, while that of soy based formulas was considerably lower (45.0±8.3 mg g⁻¹ protein). In vitro protein digestibility values ranged 85.5–88.9% for soy-based formulas and 90.5–98.3% for formulas based on dairy proteins. Formulas based on milk enriched with whey had higher lactulose content than those based on cow's milk. However, all values were below the limit of 600 mg L⁻¹ recommended for UHT milk.     

Formation of hydroxymethylfurfural and furosine during the storage of jams and fruit-based infant foods

Simultaneous formation of hydroxymethylfurfural (HMF) and furosine (Fu) during the storage of three batches of jam samples (one commercial and two laboratory prepared) and one of fruit-based infant food (commercial), at 20 and 35 °C during 12 months, was investigated to evaluate the reliability of the combination of both parameters as quality indicators. In general, the concentration of both indicators increased with time and temperature of storage, formation of furosine being less temperature dependent than that of HMF. HMF was proved to be a good indicator of the severity of heating during manufacture and/or inadequate temperature during prolonged storage, whereas furosine may be a useful indicator of the storage conditions. The combination of both indicators can afford important information on the quality of jams and fruit-based infant foods during processing and storage.     

Synthesis of galactooligosaccharides using sweet and acid whey as a substrate

Two commercial available lactases from Aspergillus oryzae and Kluyveromyces lactis were used to study the synthesis of galactooligosaccharides (GOS) in sweet and acid whey. At 38 g L⁻¹ initial lactose concentration, the A. oryzae enzyme gave a GOS yield of 10.91 ± 0.01% in lactose solution, 10.93 ± 0.18% in sweet whey and 11.32 ± 0.59% in acid whey. Thus, the components in whey did not influence the enzymes transgalactolytic activity. On the other hand, the K. lactis enzyme showed a strong dependence on whey type and whey concentration. At 38 g L⁻¹ initial lactose concentration, GOS yields were 10.93 ± 0.26% in lactose solution, 4.30 ± 0.17% in sweet whey and 10.56 ± 0.41% in acid whey. However, with increasing initial lactose concentration, the inhibitory effect of sweet whey was decreasing, which resulted in even higher yields than in lactose solution.     

Evaluation of furosine,lactulose and acid-soluble β-lactoglobulin as time temperature integrators for whipping cream samples at retail in Austria

Three heat load indicators, i.e., furosine, lactulose and acid-soluble β-lactoglobulin, were determined in whipping cream samples purchased from Austrian market (n = 33), as well as commercial samples obtained directly from one Austrian dairy company (one brand, n = 25). Furosine contents were 47.8 ± 14.0, 72.2 ± 36.6, and 172.5 ± 17.7 mg 100 g⁻¹ protein, and β-lactoglobulin contents were 143 ± 91, 195 ± 150, and 89 ± 31 mg L⁻¹ for retailed pasteurised, extended shelf life (ESL), and ultra-high temperature (UHT) cream samples, respectively. Lactulose concentrations (analysed enzymatically) were 29 ± 10, 56 ± 41, and 201 ± 24 mg L⁻¹ for pasteurised, ESL and UHT cream samples, respectively. Linear correlation obtained for furosine and lactulose concentrations indicated that these indicators can reliably assess the heat load of pasteurised, ESL and UHT cream samples, whereas β-lactoglobulin was definitely not appropriate to discriminate between these heating categories.     

Combined use of HMF and furosine to assess fresh honey quality

BACKGROUND: The quality of honey can be affected by practices such as adulteration, inadequate storage or the application of severe heat treatments. Because hydroxymehylfurfural (HMF) is an indicator of honey freshness and furosine (ε‐2‐furoylmethyl lysine) has proved to be a useful chemical indicator of the progress of the Maillard reaction in foods, the aim of this work was to assess their usefulness as indicators of fresh honey quality. The effect of heat treatment, storage and adulteration with different types of syrups on HMF and furosine content has been studied. RESULTS: In fresh honey, HMF and furosine values ranged from 0.9 to 14.6 mg kg^?1 of product and from 3.06 to 12.06 g kg^?1 of protein, respectively. Heating of honey samples with different pH (3.76 and 5.14) produced slight increases in HMF content and negligible changes were detected in furosine values. The storage of fresh honey for 2 years caused a high increase in the HMF level, reaching values above EU limits. However, furosine showed a different behavior depending on the type of honey sample. Adulteration assays using different syrups produced an increase in HMF and a decrease of furosine values by dilution effect. HMF content of adulterated honey samples with syrup of known origin did not exceed EU limits. CONCLUSION: These results show the influence of long periods of storage or adulteration, using different percentages of corn or invert sugar syrups, on HMF and furosine content of fresh honey. This seems to indicate that the combination of HMF and furosine may be useful for evaluating the quality of fresh honey. Copyright © 2009 Society of Chemical Industry     

Influence of protein concentration on surface composition and physico-chemical properties of spray-dried milk protein concentrate powders

Surface composition, moisture sorption behaviour and glass–rubber transition temperature (T_gr) were determined for spray-dried milk protein concentrate (MPC) powders over a range of protein contents (35–86 g 100 g⁻¹). Surface characterisation of MPC powders indicated that fat and protein were preferentially located on the surface of the powder particles, whereas lactose was located predominantly in the bulk. Moisture sorption analysis at 25 °C showed that MPC35 exhibited lactose crystallisation, whereas powders with higher protein contents did not and continually absorbed moisture upon humidification up to 90% RH. The GAB equation, fitted to sorption isotherms of MPCs, gave increases in monolayer moisture value (m_m) with protein content. T_gr, measured with a rheometer, decreased significantly (P < 0.05) with increasing water content and increased with increasing protein content (P < 0.05). In conclusion, increasing protein concentration of MPCs resulted in altered surface composition and increased m_m value and T_gr values.     

Occurrence of furosine and hydroxymethylfurfural as markers of thermal damage in dehydrated vegetables

The presence of furosine and hydroxymethylfurfural (HMF) as markers of thermal damage in commercial dehydrated vegetables has been studied. Furosine was measured in all the analysed samples whereas HMF was detected only in garlic, onion, and tomato groups and some other individual vegetables. Furosine, as indicator of the first steps of the Maillard reaction, ranged from 1.12 to 923 mg/100 g protein (depending on the vegetable species and thermal treatment applied) and was well correlated with the browning development in not severely heat-treated samples. In addition, the results seem to indicate that reducing sugars play an important role in the formation of furosine in some vegetable species but not HMF at the conditions used for the dehydration process. The findings of this study show the usefulness of furosine as a quality indicator for sensitive control of the dehydration process in vegetables.     

Chemical composition and potential of some underutilized tropical biomass. I: fluted pumpkin (telfairia occidentalis)

The seeds of Telfairia occidentalis have been subjected to standard chemical analysis to evaluate their properties. Proximate analysis indicated a low moisture content (6.30 ± 0.50%). The ash content was slightly higher than the range recommended for compounding of animal feed (3.44 ± 0.06%). The carbohydrate content was low (16.5 ± 0.12%). Starch, however, constituted the dominant carbohydrate (62.5 ± 0.48), while three sugars, glucose, fructose and sucrose were detected in the seed. The crude protein in the seed was high (16.0 ± 0.03%), a value which compared favourably with high protein seeds and nuts. In all, 16 amino acids were detected in the protein. Glutamic acid showed the highest concentration (16.4 g 100 g⁻¹), while lysine showed the lowest (2.6 g 100 g⁻¹). The brown oil extracted from the seed (yield 48.6 ± 0.94) had the following physicochemical properties; acid value, 3.05 ± 0.80 g, saponification value 166 ± 1.34 mg/KOH g⁻¹, free fatty acids, 0.3 g and peroxide value 3.02 ± 0.07 mg Eq kg⁻¹. The iodine value (80.1 ± 0.10)g 100 g⁻¹ indicated a preponderance of unsaturated fatty acid. Four fatty acids were detected whilst unsaturated acids constituted 61.3 g. Triglyceride was the dominant lipid species while hydrocarbons, waxes, sterols and sterol esters and higher alcohols, were detected in the unsaponifable matter. Results of nutritionally valuable mineral elements indicated that potassium occurred at the highest concentration.     

Study on the sugar content of blue-veined “Gorgonzola” PDO cheese

A chromatographic method, HPAEC-PAD, was applied to 49 samples of Gorgonzola PDO cheese to quantify residual sugars. Very low levels were detected in both sweet and piquant categories: values were, respectively, 1.24 ± 1.30 and 0.69 ± 0.11 mg 100 g⁻¹ for lactose, 1.21 ± 0.60 and 2.07 ± 1.77 mg 100 g⁻¹ for galactose and 5.41 ± 4.58 and 4.46 ± 4.09 mg 100 g⁻¹ for glucose. Analysis of cores, taken from the same cheese at different days of ripening, showed that sugars had already been completely metabolised 10 days after production. These results allow the use of term “naturally lactose free” for Gorgonzola PDO cheese. The chromatographic profile showed the presence of other peaks, which were tentatively identified as polyols (sugar alcohols), probably derived by metabolism and catabolism of microflora.     

Possible adducts formed between hydroxymethylfurfural and selected amino acids,and their release in simulated gastric model

This work aimed to investigate the reactivity of hydroxymethylfurfural (HMF) with selected amino acids, to identify the produced adducts and to clarify whether or not the adducts release HMF after their digestion under gastric conditions. Results showed that cysteine, glycine and lysine can deplete the added HMF, and their reactivity increased with increasing pH and temperature. Cysteine (25 μmol mL^?1) depleted 91.0% of the added HMF (315.3 μg mL^?1) at 40 °C in 15 min, lysine did not eliminate HMF until 80 °C, and glycine started to eliminate HMF at 100 °C. Four adducts for cysteine, three adducts for lysine and only one adduct for glycine were identified through HPLC–MS–MS after they reacted with HMF. The adducts formed from the reaction mixture of cysteine, lysine and glycine with HMF only released 1.7%, 2.6% and 10.5% of eliminated HMF, respectively, after their digestion in simulated gastric conditions.     

Effect of partial replacement of sodium chloride with potassium chloride on the characteristics of Minas Padrão cheese

Partial replacement of NaCl by KCl (25% and 50%) in Minas Padrão cheese was investigated for the physicochemical characteristics, sensory evaluation, fatty acid profile, and texture parameters. Salt replacement did not affect the moisture content, protein, fat, ash, water activity, chloride, pH, and proteolysis. A significant reduction in sodium levels was observed, ranging from 369.12 mg 100 g⁻¹ to 210.05 mg 100 g⁻¹, while the control treatment (100% NaCl) presented 608.67 mg 100 g⁻¹. Proteolysis indexes increased throughout ripening. Hardness and chewiness increased, as a result of pH reduction and syneresis in cheese, which caused a decrease in moisture content. The fatty acid profile was affected by sodium reduction, with an increase in short chain, medium-chain, and polyunsaturated fatty acids. In relation to the acceptance test, no significant differences were observed for the cheese with a substitution of 25% sodium chloride with potassium chloride when compared with the control.     

Lactose,glucose and galactose content in milk,fermented milk and lactose-free milk products

Lactose, glucose and galactose contents in milk and fermented milk products and their lactose-free alternatives, were determined. Storage of products up to the best-before dates had no effect on carbohydrate composition. Total galactose content in yoghurt, i.e., free galactose plus the galactose moiety of lactose, was 2.3–2.4 g 100 g⁻¹ (94–95% of that in milk), whereas that in Swedish soured milk and kefir was 1.9–2.0 g 100 g⁻¹ (75–79% of that in milk). Lactose levels in lactose-free milk and fermented milk products were below or close to detection limits for all products. Only small differences in total galactose content existed for the lactose-free alternatives of milk, yoghurt and filmjölk, all with average total galactose contents of 1.3–1.4 g 100 g⁻¹ (55–60% of that in milk). In contrast, lactose-free kefir had the same galactose content as milk, 2.4 g 100 g⁻¹.     

The prediction of moisture sorption isotherms for dairy powders

Moisture sorption isotherms were measured for whey protein isolate, high micellar casein and a milk protein concentrate powder. No temperature dependence was observed over the temperature range of 4–37 °C. At 50 °C the powders absorbed less moisture than observed at the lower temperatures. These isotherms were used to predict the isotherms for freeze-dried amorphous lactose/casein/whey protein powders. An isotherm for micellar casein was predicted using a simple additive isotherm model and was used along with isotherms for whey protein and amorphous lactose to predict moisture sorption isotherms for commercial dairy powders. Predicted isotherms compared well with measured isotherms indicating that this simple additive isotherm model is suitable for predicting moisture sorption isotherms of dairy powders. Delayed lactose crystallisation was observed in lactose/whey protein powders when compared to lactose/casein powders over the same water activity range.     

Economic aspects of cheese making as influenced by whey processing options

Economic consequences of the cheese making process are illustrated through several sample calculations concerning processing of whey in relation to cheese making throughput and several whey processing alternatives. Small cheese plants with daily milk throughput of approximately 100 000 kg cannot economically justify the capital for water removal equipment. For small plants that have to convert whey to a dry product, alternatives include pre-concentrating with a reverse osmosis unit or a small plate evaporator and drying on a double roller dryer. The economics are evaluated at several price levels. At the upper scale of cheese plant size (2–3 million kg d⁻¹ of milk), the investment for whey processing is about half the total investment. Cash flows are calculated for electricity, natural gas and whey powder prices. Increased investment for further processing into whey protein concentrate and dried whey solubles or lactose is evaluated at several price levels.     

Fluorescence associated with Maillard reaction in milk and milk-resembling systems

The progress of the Maillard reaction in milk and milk-resembling systems during heating was followed by monitoring free fluorescent intermediary compounds. Fluorescence intensity was examined over a wide temperature/time range (90–140 °C/0.5–30 min). Different kinetic behaviours were found in the presence or absence of amino groups in the system. Traces of fluorescence were detected when the lactose system without proteins was heated; the isomerization and degradation reactions of lactose could also generate fluorescent compounds. Fluorescence accumulation in the lactose system (without proteins) proceeded according to first-order reaction kinetics, whereas systems with lactose and casein, lactose and whey protein and milk fitted zero-order reaction kinetics. Apparent activation energies calculated were 61.3, 78.6, 59.6 and 83.9 kJ mol⁻¹ for lactose system, lactose/casein system, lactose/whey protein system and milk, respectively. Moreover, levels of intermediary fluorescent compounds in Spanish commercial milk (pasteurized, UHT-treated and in-bottle sterilized milk) have been studied.