Effects of prolonged heating on antioxidant activity and colour of honey

The kinetics of changes in total antioxidant activity as assessed by DPPH radical and brown pigment formation (BPF) in honey heated at different temperatures (50, 60 and 70 °C) for up to 12 days were studied. Antioxidant activity and BPF increased with treatment temperature and time. BPF increased following zero-order kinetics with the activation energy value of 122 kJ/mol⁻¹ at 50–70 °C. However, antioxidant activity variation showed different trends according to heating temperatures following second-order, first-order and zero-order kinetics at 50, 60 and 70 °C, respectively. Heating of honey at 70 °C was found to be more effective than 50 and 60 °C for both two parameters. The results demonstrated that antioxidant activity was correlated with increased browning of the samples.     

Ultrasound-assisted production of bioethanol by simultaneous saccharification and fermentation of corn meal

An ultrasound-assisted liquefaction as a pretreatment for bioethanol production by simultaneous saccharification and fermentation (SSF) of corn meal using Saccharomyces cerevisiae var. ellipsoideus yeast in a batch system was studied. Ultrasound pretreatment (at a frequency of 40 kHz) was performed at different sonication times and temperatures, before addition of liquefying enzyme. An optimal duration of the treatment of 5 min and sonication temperature of 60 °C were selected, taking into account glucose concentration after the liquefaction step. Under the optimum conditions an increase of glucose concentration of 6.82% over untreated control sample was achieved. Furthermore, the SSF process kinetics was assessed and determined, and the effect of ultrasound pretreatment on an increase of ethanol productivity was investigated. The obtained results indicated that the ultrasound pretreatment could increase the ethanol concentration by 11.15% (compared to the control sample) as well as other significant process parameters. In this case, the maximum ethanol concentration of 9.67% w/w (which corresponded to percentage of the theoretical ethanol yield of 88.96%) was achieved after 32 h of the SSF process. A comparison of scanning electron micrographs of the ultrasound-pretreated and untreated samples of corn meal suspensions showed that the ultrasound stimulated degradation of starch granules and release of glucose, and thereby accelerated the starch hydrolysis due to the cavitation and acoustic streaming caused by the ultrasonic action.     

Quality of honeys influenced by thermal treatment

Honey producers have been heating honeys at mild temperatures below 100 °C chiefly in order to prevent post-bottling crystallization. In this study, we aimed to determine the effects of thermal treatment on the HMF content of honeydew and floral honey during the isothermal heating process at mild temperatures. Water content, formol number, total acidity, pH value and minerals were also determined in both honey types as their characteristics differ with composition, which is able to affect the rate of HMF formation. Potassium content and pH value were found as the distinguishing properties and both were greater in honeydew honey than in floral honey (p<0.01). Honeydew and floral honey samples were heated at 75, 90 and 100 °C for 15-90 min and analysed for HMF content by HPLC-RP. The Arrhenius model was used to calculate reaction rate constants and activation energies which were found to be different for each of the honey types. Heating at 90 °C for up to 90 min in floral honeys and up to 75 min in honeydew honeys did not cause a significant increase of HMF and not exceed the threshold level of 40 mg kg⁻¹. Our results show that the excessive HMF content might be related to primitive storage conditions rather than overheating.     

Honey diastase activity modified by heating

Diastase activity is a honey quality parameter used to determine if honey has been extensively heated during processing. Honey heating effect on the diastase activity was studied in two steps. Heating was carried out in the transient heating step, with final temperatures between 60 and 100 °C and 14 s elapsed time, and in the isothermal heating step, in which temperature was held between 60 and 100 °C at heating times between 120 to 1200 s. Six honey samples with initial diastase activity between 25.8 and 11.2 Schade units were tested. During the transient heating, it was observed a decrease in the diastase activity related to an increase in temperature in all assays. The activity becomes zero at 100 °C for both transient and isothermal heating. During isothermal heating, all samples showed a decrease of the diastase activity at short heating times. However, an activity recovery occurs in medium temperature treatments at longer times. The initial activity value, corresponding to the control sample, was not achieved in any case. This changing behaviour makes diastase activity an uncertain parameter to determine if honey has been submitted to heating.     

Hydroxymethylfurfuraldehyde and amylase contents in Australian honey

The quality of Australian honey samples (processed and unprocessed) was assessed using HPLC techniques. 5-Hydroxymethylfurfuraldehyde (HMF) was used as the main quality indicator. Sampling included four commercially-processed honeys (Australian rainforest, Beechworth, Homebrand and Leabrook) and three unprocessed (Banksia, Grey box and Mallee). All honey samples, except Leabrook and Beechworth, showed an initial HMF content less than the Codex Alimentarius and International Honey Commission standard (40 mg/kg). HMF contents in Leabrook and Beechworth were 50.8 ± 1.34 and 74.9 ± 2.34 mg/kg, respectively. Heating unprocessed honey at 85 °C for 2 min caused significant (p ? 0.05) increment in HMF contents. The amounts of HMF in Mallee samples increased from 34.0 ± 0.31 to 42.3 ± 0.37 mg/kg after 2 min at 85 °C. All honey samples showed amylase activity above the minimum limit (8 Gothes). The physiochemical properties of honey showed significant variations among samples. The results revealed also that heating was not the only factor influencing HMF formation in honey, but also honey composition, pH value and floral source can contribute to these variations. Consequently, the amount of HMF may be an insufficient sole indicator of honey quality.     

Effect of processing temperature on tenderness,colour and yield of beef steaks subjected to high-hydrostatic pressure

Our aim was to achieve a single-step pressure-heat process that would produce tender, juicy beef steaks from meat that would otherwise be tough when cooked. Steak portions (25 mm thick) from hind-quarter muscles were subjected to heat treatment at 60, 64, 68, 72 or 76 °C for 20 min, with or without simultaneous application of high pressure (200 MPa). Control steaks were heated at 60 °C for 20 min with or without pressure and cooked at 80 °C for 30 min. Compared with heat alone, pressure treatment resulted in higher lightness scores at all temperatures and overall yield was improved by pressure treatment at each temperature. Even at 76 °C, the overall water losses were < 10% compared with > 30% for heat alone. Meat tenderness (peak shear force) was improved for the pressure–heat samples at temperatures above 64 °C, and was optimal at 76 °C. Therefore, subject to microbial evaluation, this single-step pressure-heat process could be used to produce tender, high moisture content steaks ready for consumption.     

The impact of ultrasound decrystallization on enzymatic,antioxidant and antibacterial properties of honey

The aim of the research was to assess the impact of liquefying honey by ultrasound processing on its biological activity. Four solid honey samples of different botanical origin were decrystallized by using the ultrasound (sonic bath, 40 kHz, 800 W) and conventional thermal processing (water bath, 40 °C). The biological properties of liquefied and control solid honeys were compared. The ultrasound processing significantly shortened the time of honey liquefaction (from 24 h to 15 min) and delayed of the re-crystallization process compared to conventional method (from 1 to 4 months). Diastase number was comparable in ultrasound and unprocessed honeys, but decreased in conventionally liquefied samples (by 8 to 20.6%) whereas the activity of α-mannosidase and β-galactosidase was insignificantly affected only. Growth inhibition of S. aureus and E.coli by 12.5% water solution of control honey samples was variety-dependent, the lowest for rape (12 and 19%) and the highest for honeydew (32 and 38%, respectively). No significant changes were observed after ultrasound treatment. The antioxidant properties of ultrasound processed honeys were insignificantly reduced up to 8%, while total polyphenols content increased by 3–6% in 75% of tested samples. The hydroxymethylfurfural (HMF) content significantly increased after both treatments (from 31 to 40%), however without exceeding the allowable limit.Industrial relevanceHoney crystallization during storage is natural but undesirable serious problem in processing and marketing of the honey. The ultrasound processing shortened the processing time (saved costs), limited the honey biological activity deterioration, and delayed the re-crystallization of processed honeys. Ultrasound processing is a beneficial non-thermal alternative for conventional liquefying of honey by heating.     

Soymilk treated by ultra high-pressure homogenization: Acid coagulation properties and characteristics of a soy-yogurt product

The effects of ultra high-pressure homogenization (UHPH) on soymilk were investigated and its suitability for soy-yogurt manufacturing was compared with conventional heat treatments (UHT and autoclaved). UHPH soymilk at 40 and 50 °C inlet temperature was treated at 200 and 300 MPa. Coagulation parameters and acidification curves were determined for the fermentation process. Textural parameters, water-holding capacity and microstructure were performed on soy-yogurts obtained after cold storage during 24 h. Results indicated that conventionally heat-treated soymilks and UHPH-treated samples exhibited different behaviour to coagulation. Heat-treated soymilk had a shorter onset of gelation, and higher aggregation rate and gel network density than UHPH-treated soymilk. However, physical quality parameters, specially firmness, were much better in UHPH than in conventional heat-treated soy-yogurts.     

Inactivation of Cronobacter sakazakii by manothermosonication in buffer and milk

The inactivation of Cronobacter sakazakii by heat and ultrasound treatments under pressure at different temperatures [manosonication (MS) and manothermosonication (MTS)] was studied in citrate-phosphate pH 7.0 buffer and rehydrated powdered milk. The inactivation rate was an exponential function of the treatment time for MS/MTS treatments (35−68 °C; 200 kPa of pressure; 117 μm of amplitude of ultrasonic waves) in both media, and for thermal treatments alone when buffer was used as heating media. Survival curves of C. sakazakii during heating in milk had a concave downward profile. Up to 50 °C, the lethality of ultrasound under pressure treatments was independent of the treatment temperature in both media. At temperatures greater than 64 °C in buffer and 68 °C in milk, the inactivating effect of MTS was equivalent to that of the thermal treatments alone at the same temperature. Between 50 and 64 ºC for buffer and 50 and 68 °C for milk, the lethality of MTS was the result of a synergistic effect, where the total lethal effect was higher than the lethal effect of heat added to that of ultrasound under pressure at room temperature. The maximum synergism was found at 60 °C in buffer and at 56 °C in milk. A heat treatment of 12 min (60 °C) or 4 min of an ultrasound under pressure at room temperature treatment (35 °C; 200 kPa; 117 μm) would be necessary to guarantee the death of 99.99% of C. sakazakii cells suspended in milk. The same level of C. sakazakii inactivation can be achieved with 1.8 min of a MTS treatment (60 °C; 200 kPa; 117 μm). Damaged cells were detected after heat treatments and after ultrasound under pressure treatments at lethal but not at non-lethal temperatures.     

Effects of high pressure/thermal treatment on lipid oxidation in beef and chicken muscle

Lipid oxidation was studied in beef and chicken muscle after high pressure treatment (0.1–800 MPa) at different temperatures (20–70 °C) for 20 min, prior to storage at 4 °C for 7 days. Pressure treatment of beef samples at room temperature led to increases in TBARS values after 7 days storage at 4 °C; however, the increases were more marked after treatment at pressures ?400 MPa (at least fivefold) than after treatment at lower pressures (less than threefold). Similar results were found in those samples treated at 40 °C, but at 60 °C and 70 °C pressure had little additional effect on the oxidative stability of the muscle. Pressure treatments of 600 MPa and 800 MPa, at all temperatures, induced increased rates of lipid oxidation in chicken muscle, but, in general, chicken muscle was more stable than beef to pressure, and the catalytic effect of pressure was still seen at the higher temperatures of 50 °C, 60 °C and 70 °C. The addition of 1% Na₂EDTA decreased TBARS values of the beef muscle during storage and inhibited the increased rates of lipid oxidation induced by pressure. The inhibition by vitamin E (0.05% w/w) and BHT (0.02% w/w), either alone or in combination, were less marked than seen with Na₂EDTA, suggesting that transition metal ions released from insoluble complexes are of major importance in catalysing lipid oxidation in pressure-treated muscle foods.     

The role of polyphenol oxidase and peroxidase in the browning of water caltrop pericarp during heat treatment

The mechanism of browning involving enzymatic browning was investigated in the pericarp of water caltrop, an Asian vegetable popular for its taste and medicinal properties. Polyphenol oxidase (PPO) and peroxidase (POD) activities were determined in pericarp at various times and temperatures. Water caltrop consisted of 44.22% moisture content, 37.23% crude fibre, and 2.63% crude protein. PPO and POD activities dropped from 62 and 38 units/g sample, respectively, as water temperature was increased from 30 to 80 °C. Optimum pH and temperature for PPO activity was at pH 5.0, 25–45 °C, and POD activity peaked at 60 °C. High PPO and POD activities at 40–50 °C resulted in degradation of phenolic compounds, which led to increased aggregation of browning pigments and discolouration (lower L-values) of the pericarp. Enzymatic browning was determined as the major factor in the browning discolouration of heat-treated water caltrop pericarp.     

Feeding heat-treated colostrum or unheated colostrum with two different bacterial concentrations to neonatal dairy calves

The objective of this study was to determine the effects of feeding heat-treated colostrum or unheated colostrum of different bacterial counts on passive transfer of immunity in neonatal dairy calves. First milking colostrum was collected from Holstein cows, frozen at -20°C, and then thawed and pooled into a single batch. One-third of the pooled colostrum was transferred into plastic containers and frozen at -20°C until needed for feeding (unheated-low bacteria). Another third was heat-treated at 60°C for 30 min and then frozen at -20°C until needed for feeding (heat-treated). The final third of colostrum was transferred into plastic containers, stored at 20°C for bacteria to grow for 24 h (unheated-high bacteria), and then frozen at -20°C until needed for feeding. A total of 30 Holstein bull calves weighing ≥30 kg at birth were systematically enrolled into 1 of the 3 treatment groups. Calves were separated from their dams at birth before suckling occurred. Before colostrum was fed, a jugular blood sample was collected from each calf. The first feeding consisted of 3.8 L of colostrum containing, on average, 68 g of IgG/L using an esophageal feeder between 1.5 and 2 h after birth. For the second and third feeding pasteurized whole milk at 5% of birth weight was fed. Blood samples were collected before colostrum feeding and at 24 and 48 h of age to determine serum total protein (STP) and IgG concentrations. Heat treatment of colostrum at 60°C for 30 min reduced colostrum bacteria concentration yet maintained colostral IgG concentration and viscosity at similar levels to the control treatment. Calves fed heat-treated colostrum had significantly greater STP and IgG concentrations at 24 h and greater apparent efficiency of absorption (AEA) of IgG (STP = 62.5 g/L; IgG = 26.7 g/L; AEA = 43.9%) compared with calves fed unheated-low bacteria colostrum (STP = 57.0 g/L; IgG = 20.2 g/L; AEA = 35.4%) or unheated-high bacteria colostrum (STP = 56.2 g/L; IgG = 20.1 g/L; AEA = 32.4%). High bacteria load in colostrum did not interfere with total protein or IgG absorption or AEA.     

Effects of heat treatment and high pressure on the subsequent lactosylation of β-lactoglobulin

The effects of a previous heat treatment (60 and 80 °C, 30 min) and high-pressure (400 MPa, 25 and 60 °C, 1 h) on the subsequent lactosylation of β-lactoglobulin (50 °C, 44% RH, 120 h) were investigated. A control of native β-lactoglobulin was also stored under the afore-mentioned conditions. The structural changes caused during these treatments were studied by the loss of amino groups, SE-HPLC and native-PAGE and the degree of lactosylation was evaluated by means of furosine determination. After thermal and high-pressure treatments, the greatest structural changes were observed in the case of samples of β-lactoglobulin treated at 80 °C, 30 min and 400 MPa, 60 °C, 1 h. During storage, the highest lactosylation degree was found in native β-lactoglobulin. In heat-treated samples, the increase of lactosylated lysines was lower than the decrease of free amino groups, probably due to the cross-linking reactions. A similar decrease of free amino groups of β-lactoglobulin was observed immediately after 400 MPa, 60 °C, 1 h and 80 °C, 30 min; however, the level of lactosylation during the storage period was lower in the former, indicating different types of conformational changes in the two treatments. These differences lead to a higher effectiveness of heat-treatment than high-pressure in denaturating β-lactoglobulin for subsequent lactosylation under the tested conditions (of temperature, time, high-pressure and storage).     

Evaluation of physical properties during storage of set and stirred yogurts made from ultra-high pressure homogenization-treated milk

The effects of ultra-high pressure homogenization (UHPH) on cow's milk were investigated and its suitability for yogurt manufacturing was compared with the conventional process currently applied in the yogurt industry. Yogurts were prepared from UHPH-treated milks at 200 and 300 MPa at 40 °C, and yogurts prepared from heat-treated milk at 90 °C for 90 s, homogenized at 15 MPa and enriched with 3% of skim milk powder were used as control samples. This study included determination of titrable acidity, water-holding capacity (WHC), and textural and rheological evaluation of gels in both set-type and stirred yogurts. In order to follow the evolution of yogurts during storage at refrigeration temperature (4–6 °C), all analyses were carried out weekly (1, 7, 14, 21 and 28 days). Results showed that yogurts from UHPH-treated milk presented higher WHC and firmness values compared with the conventional yogurts. However, the disruption of the network from UHPH-treated milk into stirred gels resulted in yogurts with higher consistency, less syneresis but coarser structure than the conventional ones.     

Rheological characterisation of cake batters generated by planetary mixing: Comparison between untreated and heat-treated wheat flours

The rheological behaviour of high ratio cake batters prepared with untreated and heat-treated wheat flours was analysed at different stages of the manufacturing process, namely slurry, (on aeration) foams and (with fat addition) aerated emulsions, featuring air volume fractions up to 0.50. Both steady shear and viscoelastic behaviours were studied. All materials exhibited shear-thinning behaviour at 20 °C over the shear rate range studied (0.07-10 s⁻¹). The generalised Cox-Merz rule could be applied to all samples. Materials prepared with heat-treated flours exhibited greater stability, as indicated by slurry thixotropy and cohesive energy, and the change in apparent viscosity and air content of foams and aerated emulsions on extended mixing. Foams and aerated emulsions showed significant elastic behaviour with G′∼G″. The temperature dependency of aerated emulsions was studied by oscillatory shear testing from 20 to 100 °C and indicated three regimes in temperature dependence: below 40 °C G′and G″ were insensitive to temperature; between 40 and 70 °C the complex viscosity exhibited Arrhenius-type behaviour, while above 70 °C G′ and G″ increased as expected for gelatinisation and foam setting. The weak gel model for foods was used to analyse the latter data sets and confirmed that the gel network generated in aerated emulsions prepared with heat-treated flours was significantly stronger than those made with unheated flours. The differences between flour types were also observed in tests on un- and heat-treated flours obtained from a second and third harvest. The impact of these quantifiable differences in rheology on performance during baking is discussed.     

Fat oxidation in freeze-dried grouper during storage at different temperatures and moisture contents

The effects of moisture content levels and storage temperature on the lipid oxidation in freeze-dried grouper were studied. Three trends were observed in the changes of PV (peroxide value) depending on the moisture content and storage temperature. An exponential rise of PV was observed (p < 0.05) at lower temperatures (−20 °C and 5 °C for samples at moisture 5 g/100 g; and −20 °C for samples at moisture 20 g/100 g). At temperatures 25 °C for samples at moisture 5 g /100 g, and 5 and 25 °C for samples at 20 g moisture/100 g peaks of PV were observed (p < 0.05). At higher temperatures (40 °C for both moisture content levels) an exponential decay instead of increase were observed (p < 0.05). Moisture content levels had no significant effect (p > 0.05) on PV stored at temperature of −40 °C. The monolayer moisture for freeze-dried grouper was estimated as 6.2 g/100 g dry solids using BET-isotherm. Differential scanning calorimetry (DSC and modulated DSC) thermogram line showed two shifts (i.e. glass transition) and two endothermic peaks, one for melting of oil and another for decomposition. The validity of the water activity and glass transition concepts were evaluated. It is concluded that glass transition concept may be used to explain the process more adequately.     

Proteolysis of yogurts made from ultra-high-pressure homogenized milk during cold storage

Proteolysis was investigated in yogurts made from milk that was ultra-high-pressure homogenized at 200 or 300 MPa and at 30 or 40°C and compared with those produced from heat-treated milk containing 3% skim milk powder. To evaluate changes in the protein fraction, samples were analyzed at d 1, 7, 14, 21, and 28 of storage for residual caseins, peptides, and total free amino acids. Results showed that yogurts from heat-treated milk and 300 MPa-treated milk presented similar levels of residual caseins, as well as similar profiles of soluble peptides and total free amino acids. On the contrary, greater amounts of hydrophobic peptides were detected in yogurts made from 200 MPa-treated milk at both 30 and 40°C, especially at the end of storage. In all treatments studied, caseins were hydrolyzed and hydrophobic peptides were increased during storage, as reflected by the increase in soluble nitrogen at the end of the storage.     

Carrot volatiles monitoring and control in microwave drying

Volatiles emanating from carrot [Daucus carota L. cv. ‘Enterprise’] samples dried in a microwave oven were monitored throughout the drying process with a zNose™. Drying temperatures were first set to 50 °C, 60 °C, 70 °C, and 80 °C. Six typical volatile peaks were recorded every 4 min for each of the three replicate runs. Color and sensory evaluation were performed after drying. Samples could be dried in a short time at high temperatures but the interior of some samples was charred. Longer time and more energy were required at low temperature drying. A fuzzy logic control system was then designed and employed to control the drying temperature throughout the whole drying process, using detected volatile peaks as variables. Based on the fuzzy logic controlled temperature curve, a simple linear control method was developed. It was shown that carrot quality was intact and time and energy were saved with these new control strategies.     

Influence of simulated industrial thermal treatments on the volatile fractions of different varieties of honey

The aim of this study was to determine if the volatile fraction of honey is affected by the application of standard industrial thermal treatment processes. Four types of Spanish honey were studied: three of floral origin (citrus, rosemary and polyfloral) and the fourth from honeydew. Each sample of honey was divided into three parts: one was left untreated, one was liquefied (at 45 °C for 48 h) and the other was both liquefied and pasteurized (at 80 °C for 4 min). All the samples analyzed were characterized to determine their melissopalynological, physicochemical (pH, moisture, total acidity, conductivity, hydroxymethylfurfural, and diastase activity), and volatile profiles. Type of honey had a greater impact on volatile fraction variations than did heat treatment. The overall volatile profile of each kind of honey permitted the classification of the honeys by botanical origin, revealing that there were practically no differences between the raw, liquefied, and pasteurized samples of each honey. These findings suggest that industrial processes conducted under controlled conditions should not significantly alter the intrinsic aroma of honey.     

Effect of honey high-temperature short-time heating on parameters related to quality, crystallisation phenomena and fungal inhibition

The effect of a unique high-temperature short-time heating treatment on natural honeys to produce both a fungi inhibition and a crystallisation delay simultaneously was evaluated. As responses to treatments, hydroxymethylfurfural content, diastase activity, fungi and yeast development, and crystallisation starting time were measured. Besides, moisture, fructose, glucose and acidity were determined.Heating can produce a decrease in honey quality, which is made evident by a simultaneous reduction in the diastase activity, referred to as diastase number, and an increase in the hydroxymethylfurfural content. Considering the minimum admissible diastase number and the maximum admissible hydroxymethylfurfural content values, according to honey present regulations, several thermal treatment tests were performed on selected honey samples without exceeding those values. Tested conditions were: heating between 140°C and 80°C at times between 60 to 15 s and 30 to 10 s during both transient and isothermal heating stages, respectively. In all tests the diastase number was the most heat-sensitive parameter. The boundary thermal treatment, assumed as the most severe conditions able to produce a permissible quality loss, was found to be 140°C, during 15 s in the transient stage and 30 s in the isothermal stage. Beyond those values, an unacceptable diastase number reduction was produced. On the other hand, it was found that a 80°C heating, during 60 and 30 s in transient and in isothermal stages, respectively, destroyed all microorganisms responsible for quality damage without spoiling honey. This was considered to be the mild or more suitable treatment condition. Twenty-six naturally contaminated honey samples heated at such conditions showed a null capacity to develop fungi and yeast. Besides, according to the storing temperature, and moisture and glucose contents, a crystallisation beginning delay between 4 and 9 weeks was obtained on four selected honeys, according to the thermal treatment applied. Several parameters previously proposed that characterise honey crystallisation tendency as fructose/glucose, glucose/moisture and (glucose-moisture)/fructose ratios were related to the time in which crystallisation starts. A new parameter, (fructose/glucose)·moisture was proposed.