Cold dryer as novel process for producing a minimally processed and dried meat

In this study, it was aimed to design a novel dryer that operates at low temperature (≤20 °C) for the production of a minimally processed and dried meat, and to determine the drying characteristics of this product. Beef slices loaded into this dryer were dried at different low temperatures (10, 15 and 20 °C) and air flow rates (1, 2, 3 and 4 m/s) after pasteurization. The drying time of slices was significantly influenced by the temperatures and air flow rates. The shortest drying time that pass until reaching the final water content (40%) was found in the slices subjected to a temperature of 10 °C and an air flow rate of 4 m/s. Nine kinetic models were selected to evaluate the moisture ratio data, with regard to adjusted regression coefficient (R²), the reduced chi-square (χ²) and root mean square error (RMSE). Page model exhibited the best fit (R² ≥ 0.9961; χ² ≤ 0.0002 and RMSE ≤ 0.0125). In addition, the effective moisture diffusivity (D_eff) and activation energy (E_a) values of slices were 7.13 × 10⁻¹⁰ m²/s and 44.96 kJ/mol, respectively. Consequently, the low drying temperature could shorten the drying time of beef because the driving force for mass transfer is supplied by the moisture difference between food and the air in the dryer.Industrial relevanceThe novel dryer could carry out minimal processing to the meat, provide food safety and perform drying in cold conditions (≤20 °C). Beef slices dried faster with a drying temperature of 10 °C and an air flow rate of 4 m/s in this dryer. Various dried products also could be obtained by cold drying method without the loss of their quality properties.     

Properties of polyphenol oxidase in mango (Mangifera indica) kernel

Polyphenol oxidase (PPO) activity of filtered extract of ground mango kernel suspension (400 g litre⁻¹) was studied spectrophotometrically at 420 nm using catechol as substrate. The enzyme was most active at pH 6·0 and 25°C. Activity was reduced by 50% at pH values of 5·0 and 7·1, and also at temperatures of 14°C and 30°C. The calculated activation energy and the Michaelis constant (K_m) were 21·4 kcal mol⁻¹ °C⁻¹ and 24·6 mM , respectively. The V_max value was 2·14 units g⁻¹ mango kernel. The time to heat inactivate PPO decreased rapidly to < 10 min with increasing temperature of ⩾ 70°C at 50% activity. © 1998 SCI.     

Application of simulation in determining suitable operating parameters for industrial scale fluidized bed dryer during drying of high impurity moist paddy

A systematic approach has been developed for selecting the suitable drying parameters to be used for drying of high moisture and high impurity paddy with an industrial fluidized bed paddy dryer (10–20 t h⁻¹ capacity) based on targeted specific air flow rate and residence time during two typical paddy drying seasons. A mathematical model was developed by modifying an existing model and was simulated and validated with observed industrial drying data as well as data reported in the literature. Comparison between the observed and simulated results showed that the mathematical model is capable of predicting outlet paddy moisture content and air temperature well. Suitable operating parameters were determined for reducing any initial paddy moisture content (mc) down to 24–25% dry basis (db), the safe mc level after fluidized bed drying to maintain rice quality, to achieve maximum possible throughput capacity of the dryer with corresponding energy consumption. Based on these criteria, bed thickness at 10 cm, specific air flow rate of 0.05 kg kg⁻¹ s⁻¹ (for corresponding bed air velocity of 2.3 m s⁻¹), air temperature of 150 °C and residence time of 1.0 min were found to be suitable drying conditions for reducing paddy mc from 30 to 24.30% (db) in one season while the maximum throughput capacity of 15.7 tonne per hour (t h⁻¹) might be achieved. The specific electrical and thermal energy were 0.48 and 6.15 MJ kg⁻¹ water evaporated, respectively. On the other hand, the dryer capacity was found to be limited to 7.4 t h⁻¹ during drying paddy of higher initial mc (35% db). This approach might provide easy and comprehensive guidelines for selecting suitable sets of operating parameters for any industrial fluidized bed dryer at its possible maximum throughput capacity for drying of freshly harvested high moist paddy with a high level of impurities.     

Development of infrared-assisted hybrid solar dryer for drying pineapple slices: Investigation of drying characteristics,mass transfer parameters,and quality attributes

The research aims to the development and performance evaluation of an infrared-assisted hybrid solar dryer (IR-HSD) for drying pineapple slices. The IR-HSD contains an evacuated tube solar collector, blower assembly, drying chamber, infrared heater, phase change material (PCM) chamber, etc. The study investigates and compares the thermal profiling, drying kinetics, mass transfer parameters and quality attributes of pineapple slices dried using different methods, such as direct drying, phase change material (PCM)-assisted drying, PCM + IR-assisted drying, and sun drying. The average temperatures achieved inside the drying chamber for direct drying and PCM-assisted drying were 60.16 °C and 57.29 °C, respectively, while the temperature reached 60 °C for PCM + IR assisted drying. The average drying rate in PCM + IR drying was higher than in direct and PCM-assisted drying methods. The best-fitting models were the Modified Page model for direct and PCM + IR-assisted drying and the Midilli-Kucuk model for PCM-assisted and sun drying. The higher effective moisture diffusivity for PCM + IR-assisted drying was 2.59 × 10⁻⁹ m²/s, followed by direct and PCM-assisted drying. Similarly, the convective mass transfer coefficient obtained was 1.085 × 10⁻⁷ m/s, 8.321 × 10⁻⁸ m/s, and 1.381 × 10⁻⁷ m/s for direct, PCM-assisted, and PCM + IR-assisted drying, respectively. The superior quality attributes such as total flavonoid content (TFC), total phenolic content (TPC), and antioxidant activity were observed in all drying approaches with retention of colour except open sun drying, which decreased significantly. FTIR spectroscopy analysis confirmed the presence of different bioactive, including aromatic compounds, phenols and hydrocarbon functional groups. The infrared-assisted hybrid solar drying of pineapple slices showed a better drying process and quality attributes.     

The drying kinetics of kale (Brassica oleracea) in a convective hot air dryer

The effect of air temperature and sample thickness on the drying kinetics of kale was investigated using a convective air dryer at a fixed airflow rate of 1 m/s and drying air temperatures of 30, 40, 50 and 60 °C. The sliced kale leaves were dried in wire trays in 10, 20, 40 and 50 mm thick layers. The drying rate increased with drying air temperature but decreased with layer thickness. The effective diffusivity for 10 mm thick layers was found to increase with the drying air temperature and ranged between 14.9 and 55.9 × 10⁻¹⁰ m²/s. The effect of temperature on diffusivity could be expressed by an Arrhenius type relationship with a high R² of 0.9989. The activation energy of kale was found to be 36.115 kJ/mol. When four drying models were developed using the experimental data the Modified Page model was found to be marginally better than the other models in estimating the drying curve over the experimental temperature range.     

Modified Atmosphere Packaging of Fresh Beansprouts

Freshly harvested beansprouts displayed a respiration rate of about 1 mmol O₂ kg⁻¹ h⁻¹ at 10°C which was strongly dependent on temperature, a 10-fold increase being observed every 16·5°C (z=16·5°C, ie Q₁₀=4·4). This commodity is also characterised by a high initial microbial load (about 10⁷ cells g⁻¹). During storage at various temperatures from 1 to 20°C, oxygen uptake rates dramatically increased with time and this phenomenon was well correlated with the development of aerobic microorganisms which reached 10⁹ cells g⁻¹ after 2 days at 20°C or 9 days at 1°C. Beansprouts were packaged in films, with permeabilities ranging from 950 to 200000 ml O₂ m⁻² day⁻¹ atm⁻¹, and stored at 8°C. Due to plant and microbial metabolism, oxygen concentrations decreased steadily within all packs until the onset of plant tissue decay. The latter occurred after 5–6 days with the least permeable films but did not occur within when the film permeability was over 100000 ml O₂ m⁻² day⁻¹ atm⁻¹. However, such films favoured brown discolouration, exudation texture and breakdown. The orientated polypropylene film (OPP) induced anoxic condition within 2 days and favoured anaerobic metabolism and necrosis of the sprouts. In all packages there was a rapid development of aerobic microorganisms and lactic acid bacteria that resulted in the accumulation of acetate and lactate and a decrease in pH. Thus, it clearly appeared that tissue decay was enhanced by microbial activity. At 8°C, 0·24 m² of film per kg of sprouts provided the optimal atmosphere composition (ie 5% oxygen and 15% carbon dioxide) when a film permeability of 50000 ml O₂ m⁻² day⁻¹ atm⁻¹ was used. These conditions allowed a shelf-life of 4–5 days.     

Three-dimensional TLM models for water diffusion in white rice

Two, three-dimensional TLM models for water diffusion in white rice were developed. The first model consists of a three-dimensional orthogonal TLM grid with constant mesh size, the second of a two-dimensional orthogonal TLM grid with constant mesh size, using axisymmetric elements. The average mass diffusivities at 30, 40 and 50°C were estimated to be 0·875, 1·000 and 1·181 × 10⁻¹⁰m² s⁻¹ with the first model and 0·958, 1·139 and 1·319 × 10⁻¹⁰m² s⁻¹ with the second model. On the basis of an Arrhenius-type equation, the activation energy for water diffusion in white rice was calculated as 12·19 kJ mol⁻¹ and 13·03 kJ mol⁻¹ respectively for the first and the second model.     

Experimental study on drying of pear slices in a convective dryer

The experiments were conducted on pear slices with thickness of 5 mm at temperatures of 50, 57, 64 and 71 °C with an air velocity of 2.0 m s^?1. Prior to drying, pear slices were pretreated with citric acid solution (0.5% w/w, 1 min, 20 °C) or blanched in hot water (1 min, 85 °C). Also, the untreated samples were dried as control. The shortest drying time of pear slices was obtained with pretreatment with citric acid solution. It was observed that whole drying process of pear slices took place in a falling rate period. Four mathematical models were tested to fit drying data of pear slices. According to the statistical criteria (R², χ² and RMSE), the Midilli et al. model was found to be the best model to describe the drying behaviour of pear slices. The effective diffusivity of moisture transfer during drying process varied between 8.56 × 10^?11 and 2.25 × 10^?10 m² s^?1, while the activation energy of moisture diffusion in pear slices was found to be 34.95–41.00 kJ mol^?1.     

Production of a carotenoid-rich product by alginate entrapment and fluid-bed drying of Dunaliella salina

A new carotenoid-rich product was formed by entrapment of Dunaliella salina in calcium alginate beads of different alginate concentrations, followed by drying in a fluid-bed dryer. The drying process yielded β-carotene recoveries of between 79 and 89% and produced a change in the 9-cis/all-trans ratio of β-carotene isomers. The carotenoid stability of the product was dependant on both the storage conditions and alginate content (range 3·3–7·3 g litre⁻¹) of the beads. In the presence of light and oxygen total carotenoid degraded following a first order kinetic model with degradation constants between 0·016 and 0·039 days⁻¹, with the lowest degradation occurring with the lowest alginate concentration. Product stored in the dark and flushed with nitrogen produced first-order degradation constants of 0·012 and 0·020 days⁻¹ for the two higher alginate concentrations; that with the lowest alginate content showed no noticeable degradation after 58 days storage. During storage, the 9-cis isomer was significantly more unstable showing a relative loss under all conditions, degrading almost completely when stored in the presence of light and oxygen and reaching an equilibrium ratio with the all-trans isomer when stored in the dark and flushed with nitrogen. © 1998 SCI.     

Kinetics of the reaction between 3-deoxyhexosulose and sulphur(IV) oxospecies in the presence of glycine

The kinetics of the reaction between 3-deoxyhexosulose (DH) and sulphur (IV) oxospecies (S(IV)) in the presence of glycine (0·5m) at pH 5·5 and 55°C are reported. The initial reaction is of first order with respect to DH (k = 0·0164 h⁻¹) and of zero order with respect to S(IV). The presence of glycine increases the rate of reaction whilst S(IV) acts as an inhibitor through formation of the hydroxysulphonate of DH. A kinetically derived value for the dissociation constant of the hydroxysulphonate in the presence of glycine is 0·004m. Possible mechanisms and the application of the results to the S(IV)-inhibited Maillard reaction are considered.     

Performance of a solar-heated,forced-air,fully automated lumber dryer

A 3.5 m³, external collector type kiln has been designed and constructed to dry green lumber to M.C. low enough for use in furniture. The kiln uses a hot air transfer-circulation system and its ratio of collector area to lumber capacity is 2.9 m²/m³. The kiln is equipped with a fully automated supervisor system. The energy efficiency and performance of the solar kiln have been evaluated through a series of operational tests. The solar collectors operate at 71 to 75% efficiency, while the drying chamber at an efficiency of 46%. The kiln has been found able to use 33% of the available solar energy for lumber drying, Control system has been proved able to run the process to the drying gradient required by any given species of wood. The performance of the dryer, evaluated by direct comparison with air drying, is satisfactory in respect of the final moisture content and drying time. A final M.C. of 10% was attainable at all times of the year.     

Determination of convective heat transfer coefficient and specific energy consumption of potato using an ingenious self tracking solar dryer

In the present work, an attempt has been made to experimentally determine the heat transfer properties of potato in terms of convective heat transfer coefficient, specific energy consumption and specific heating rate. Drying experiments with potato cylinders have been performed in an in-house fabricated laboratory scale natural convection indirect solar dryer with self tracking mechanism. The convective heat transfer coefficient of cylindrical potato samples was evaluated by considering the combined effects of heat capacities of food product as well as radiative heat transfer from drying chamber to the food product. This study revealed that the convective heat transfer coefficient for potato cylinders was varying from 11.73 to 16.23 W/m² °C with an experimental error of 7.86 %. The specific energy consumption was decreasing exponentially with drying time, and the average value was estimated to be 3,491 kJ/kg. It was also observed that the specific heating rate for potato cylinders decrease with dimensionless moisture content.     

The dehydration of paprika with ambient and heated air and the kinetics of colour degradation during storage

The hygroscopic behaviour of dried red pepper is characterized by means of water vapour adsorption isotherms at 5, 20 and 35°C; from the GAB equation, a monolayer water content of 0·0816 kg H₂O per kg dry matter has been deduced. The effect of temperature on the drying rate of pepper is considered and yields are compared when the drying is carried out with ambient air and with different loading densities (10–40 kg m⁻²). The kinetics of paprika colour degradation during storage at different temperatures and with a moisture content corresponding to the monolayer have been studied. A sharp change in the rate of colour loss is observed at 15°C: the value Q₁₀ (°C) changes from 1·62 to 2·82 when the temperature rises above 15°C.     

Stability of Cholesterol and Paprika Carotenoids in Egg Powders as Influenced by Dietary and Processing Treatments

The effects of dietary α-tocopherol and/or oleoresin paprika (OP) on cholesterol and carotenoid stability in egg powders during spray drying and subsequent storage were investigated. Cholesterol oxidation and loss of carotenoids in eggs dried with a direct gas-fired spray dryer were greater ( P< 0·05) than in eggs dried using an indirect (electric) heating system. Dietary supplementation of α-tocopherol acetate (200 mg kg⁻¹ feed) significantly increased ( P< 0·01) the oxidative stability of cholesterol and carotenoids in eggs dried with the direct heating system. Supplementation of OP (7·5 μg g⁻¹ egg lipids) through diet or by direct addition to liquid eggs did not affect the formation of cholesterol oxidation products (COPS) during storage. However, increased concentrations of OP in liquid eggs (15 and 30 μg g⁻¹ lipids) suppressed the formation of COPS during processing and subsequent storage.     

Transport properties of liquid egg related to spray drying behaviour

The viscosities, critical moisture contents and effective water diffusivities were determined on samples of fresh and incubated liquid whole eggs at various temperatures. The liquid eggs were pretreated to simulate the possible effects of homogenisation and pasteurisation. The drying characteristics were based on measurements of weight losses against time of liquid egg films formed on glass spheres. The experimental results were used to obtain correlations appropriate for the expected temperature dependence of each property, for convenience in modelling of the spray drying operation. The ranges of the measured values are 5·6–14·5 mPa. s for coefficient of viscosity, 0·73–1·09 kg water kg⁻¹ dry matter for critical moisture content and 10–19 × 10⁻¹² m² s⁻¹ for effective water diffusivity. The results indicate similar magnitudes for the properties of fresh and incubated eggs.     

Oven drying improves the nutritional value of Calliandra calothyrsus and Gliricidia sepium as supplements for sheep given low-quality straw

Leaves from the tree legumes Gliricidia (Gliricidia sepium) and Calliandra (Calliandra calothyrsus) were fed as supplements (200 g dry matter) to sheep (n=3) given a basal diet of barley straw ad libitum. Tree leaves were fed either freshly harvested (F=fresh) or after drying at 60°C in a forced draught oven (D=dried). Voluntary intakes, digestibility and aspects of nitrogen (N) and phenolic compound metabolism were measured in all sheep. Drying decreased the condensed tannin (CT) content of Calliandra (F 117, D 82 g CT kg⁻¹ DM). Total phenolics (TP) were significantly decreased when Gliricidia was dried (F 39, D 21 g TP kg⁻¹ DM), and CT content was reduced from 20 g CT kg⁻¹ DM to zero. Sheep given Gliricidia had higher rumen ammonia concentrations (73–85 mg N litre⁻¹) than did sheep given Calliandra (37–40 mg N litre⁻¹). For both species, drying significantly increased the voluntary consumption of straw, increased DM digestibility, decreased faecal N excretion and increased N balance. For calliandra, drying decreased the apparent degradability of N in the rumen (DNR) from 0·40 to 0·28 g N g⁻¹ N ingested, and increased the apparent digestibility of N (ADN) in the post-ruminal tract from 0·20 to 0·52 g N absorbed g⁻¹ N flowing into the small intestines. For Gliricidia, DNR decreased from 0·64 to 0·51 and ADN increased from 0·41 to 0·56. There were no significant effects of drying on rates of microbial N synthesis. The above changes were discussed in relation to changes in tannin content and it was concluded that drying facilitates the formation of protein–tannin complexes which protect proteins from degradation in the rumen. These proteins are subsequently released in the small intestines, thereby promoting an increased efficiency of dietary N utilisation. ©1997 SCI     

Nonenzymatic Browning in Pear Juice Concentrate at Elevated Temperatures

The effect of temperature and soluble solids (°Brix) on nonenzymatic browning in pear juice concentrate was determined by following absorbance at 420 nm (A₄₂₀) over the temperature range of 50–80°C. Browning could be modeled as a zero order rate process with rates of 22.2 × 10⁻⁴ (45.2 °Brix), 36.9 × 10⁻⁴ (55.4 °Brix), 53.5 × 10⁻⁴ (65.1 °Brix) and 107 × 10⁻⁴ (72.5 °Brix) A₄₂₀· min⁻¹ at 80°C. Temperature dependence was described by the Arrhenius relationship with an average activation energy of 21.9 kcal · mole⁻¹. Formol titration indicated a 20% loss of amino acids during heating 4.4 hr at 80°C and no loss of carbohydrates was observed after any heating period.     

Regulation of alcoholic fermentation in batch and chemostat cultures of Kluyveromyces lactis CBS 2359

Kluyveromyces lactis is an important industrial yeast, as well as a popular laboratory model. There is currently no consensus in the literature on the physiology of this yeast, in particular with respect to aerobic alcoholic fermentation (‘Crabtree effect’). This study deals with regulation of alcoholic fermentation in K. lactis CBS 2359, a proposed reference strain for molecular studies. In aerobic, glucose-limited chemostat cultures (D=0·05–0·40 h⁻¹) growth was entirely respiratory, without significant accumulation of ethanol or other metabolites. Alcoholic fermentation occurred in glucose-grown shake-flask cultures, but was absent during batch cultivation on glucose in fermenters under strictly aerobic conditions. This indicated that ethanol formation in the shake-flask cultures resulted from oxygen limitation. Indeed, when the oxygen feed to steady-state chemostat cultures (D=0·10 h⁻¹) was lowered, a mixed respirofermentative metabolism only occurred at very low dissolved oxygen concentrations (less than 1% of air saturation). The onset of respirofermentative metabolism as a result of oxygen limitation was accompanied by an increase of the levels of pyruvate decarboxylase and alcohol dehydrogenase. When aerobic, glucose-limited chemostat cultures (D=0·10 h⁻¹) were pulsed with excess glucose, ethanol production did not occur during the first 40 min after the pulse. However, a slow aerobic ethanol formation was invariably observed after this period. Since alcoholic fermentation did not occur in aerobic batch cultures this is probably a transient response, caused by an imbalanced adjustment of enzyme levels during the transition from steady-state growth at μ=0·10 h⁻¹ to growth at μ_max. It is concluded that in K. lactis, as in other Crabtree-negative yeasts, the primary environmental trigger for occurrence of alcoholic fermentation is oxygen limitation. © 1998 John Wiley & Sons, Ltd.     

Characterization of hot air drying and microwave vacuum drying of fingerroot (Boesenbergia pandurata)

Fingerroot (Boesenbergia pandurata) was subjected to hot air drying and microwave vacuum drying. Effective moisture diffusion coefficient during the hot air drying at 60 and 70 °C were 0.2073 × 10^?10 and 0.4106 × 10^?10 m² s^?1 respectively. By using the microwave vacuum drying (13.3 kPa) at the power of 2880 and 3360 W, the effective moisture diffusion coefficient were increased to 5.7910 × 10^?10 and 6.8767 × 10^?10 m² s^?1 respectively. Based on Lewis model, drying rate constants were 0.0002, 0.0004, 0.0061 and 0.0072 s^?1 for the hot air drying at 60 and 70 °C and the microwave vacuum drying at 2880 and 3360 W respectively. Compared with the hot air drying, the microwave vacuum drying decreased drying time by 90%. Rehydration ability of the microwave vacuum dried samples was also significantly improved (P ≤ 0.05), because of porous structure. In addition, the rehydrating water of the microwave vacuum dried samples contained higher b*‐value (yellowness) than that of the hot‐air‐dried samples (P ≤ 0.05).     

Quality of enoki mushrooms as affected by packaging conditions

Fresh enoki mushrooms (100 g) were packaged under various conditions and stored at 10 °C for 14 days. Package atmosphere, weight loss, stipe elongation, surface colour and sensory quality of the mushrooms were measured during storage. Different levels of initial vacuum application did not have a significant influence on the in‐package atmosphere after 2 days. The half‐vacuum package was best in terms of quality preservation of the fresh mushrooms. A polyolefin film with respective gas permeabilities of 166 and 731 ml m⁻² h⁻¹ atm⁻¹ to O₂ and CO₂ established an equilibrated atmosphere of 1.7–2.4% O₂ and 4.1–5.6% CO₂ inside the package at 10 °C. This polyolefin film was shown to contribute to preserving the freshness of the mushrooms. Temperature fluctuations between 5 and 15 °C did not induce a harmful atmosphere inside the polyolefin package, though high temperatures accelerated the quality loss. © 2000 Society of Chemical Industry