KINETICS ON COLOR CHANGES DURING DRYING OF SOME FRUITS AND VEGETABLES

Abstract

The effect of drying conditions on color changes of apple, banana, carrot and potato during conventional and vacuum drying was investigated. The Hunder color scale parameters redness, yellowness and lightness were used to estimate color changes during vacuum and conventional drying at 50, 70 and 90°C. Air humidity during conventional drying was regulated at 15, 30 and 40%. Air temperature and humidity affected redness and yellowness, but not lightness. A first order kinetic model was fitted to experimental data adequately for both redness and yellowness. The rate of color deterioration was found to increase as temperature increased and air humidity decreased, for both drying methods and all the examined materials.     

Performance Assessment of a Potato Crisp Frying Process

Frying is a common and popular cooking method, which has been widely used in food manufacturing, though it is a very energy-intensive process. Energy analysis has been commonly used to assess the performance of fryers. In this study, we attempted to exergetically assess the performance of a potato crisp frying system, which consists of three main components, a combustor, a heat exchanger, and a fryer. In the analysis, we utilized the actual operational data obtained from the literature. We determined exergy destruction in each system component and the whole system. We calculated universal and functional exergy efficiency values for the system components and compared them with each other. We also undertook a parametric study to investigate how the overall cycle performance was affected by changing the reference environment temperature and some operating conditions. We illustrated the exergy results through the Grassmann (exergy loss and flow) diagram. We calculated the universal exergetic efficiency values of 58, 82, and 77% for the combustor, heat exchanger, and fryer, respectively, with a universal exergetic efficiency value of 4% for the whole frying system. We found that the fryer had the highest functional exergetic efficiency value of 74%, followed by the heat exchanger with 47% and the combustor with 0.08%.     

绿色马铃薯栽培技术

马铃薯是临县的主要农作物。文章从种薯选择、测土配方施肥、田间管理等方面,介绍了绿色马铃薯栽培技术,为农户生产提供借鉴。     

Impact of edible coating with or without anti-microbial agent on microbial growth during osmotic dehydration and refrigerated storage of a model plant material

The use of edible coating has proved a valuable tool in improving the efficiency of osmotic dehydration (OD) of plant material. In this study the impact of edible coating with or without an anti-microbial agent (A–M) on microbial growth was investigated. Potato cylinders (15 × 57 mm — D × L) were used as a model plant material. Calcium alginate (CA) coating was applied with or without incorporation of potassium sorbate (PS), at 0.3% of sample weight (before coating). OD took place for 3 h in stirred jars using sucrose solution at 50 °Brix and 40 °C. Microbial growth (Aerobic Plate Count — APC) was monitored both during OD (3 h) and during refrigerated storage at 5 °C (14 days). During OD, a significant reduction of the initial microbial load (ML) in the control (non-coated) treatment was observed, possibly due to a microbial “wash-out” effect. Both coating treatments resulted in a marginal decrease of initial ML in the OD product, suggesting some kind of protection against this effect. During refrigerated storage, the use of coating resulted in reaching the growth plateau several days earlier, which lead to significant reduction of maximum ML, compared to the control treatment. Besides this benefit, coating with A–M helped extend the lag phase and postpone time to reach maximum load by almost 4 days, compared to the simple coating treatment. These results can support further work on the use of more effective types and concentrations of preferably natural anti-microbials to achieve satisfactory stabilization of osmo-dehydrated/refrigerated products, without a negative impact on their minimal processing profile.

Industrial relevance

Osmotic dehydration is a very potent processing tool that has been studied extensively in terms of mass transfer phenomena. Yet, microbial studies in this area are rather scarce; thus industrial applications are very difficult to proceed, due to lack of microbial stabilization data. This is especially crucial in the case of combined, minimal processing methods, such as osmotic dehydration and refrigeration. This work is using edible coating (which is known to promote dehydration efficiency) to incorporate a common anti-microbial agent, in an effort to establish an effective series of hurdles leading to microbial stabilization of osmo-dehydrated, refrigerated products.     

Changes in glycoalkaloid and nitrate content in potatoes during dehydrated dice processing

The aim of this experiment was the determination of glycoalkaloid and nitrate content in potatoes during stages of processing into dry potato dice.Samples obtained from the tubers of three potato varieties were used: a very early Denar variety of Polish origin; Innovator, an early Dutch variety; and a Polish medium early Pasat variety. There were sampled three times from the factory store in 2009 and 2010. The potatoes were diced in laboratory conditions, by first peeling with a carborundum peeler, dicing into 10 × 10 × 10 mm pieces and rinsing with water at a temperature of 20 °C. In the next stages, the diced potatoes were blanched in water at a temperature of 75 °C for 5 min then dried in a laboratory drier for 1 h at 120 °C. After 1 h of drying, the temperature was lowered to 55-60 °C in order to obtain a defined final moisture content of 8-11%.In the raw material, intermediates and finished products, the concentrations of glycoalkaloids (α-chaconine and α-solanine) were determined using an HPLC method, and nitrates were determined colorimetrically using an RQflex analyser.It was found that the processes used in dried potato dice production significantly decreased concentrations of glycoalkaloids (α-chaconine and α-solanine) in intermediate and finished products when compared to raw material. The highest decrease in the quantity of glycoalkaloids occurred during peeling (33%) and after blanching (17%) of peeled potato. Nitrate content fell the most after cutting and rinsing with water (13%), and after blanching (23%). On average, dry potato dice contained 44% of the initial quantity of glycoalkaloids and 40% nitrate content in the final dried product.     

Inactivation kinetics for Salmonella Enteritidis in potato omelet using microwave heating treatments

The aim of this study was to model the inactivation of Salmonella enterica serovar Enteritidis in pasteurized omelet internally inoculated at different microwave heating treatments (300 W; 450 W, 600 W and 800 W). Results indicated a non significant change in Salmonella populations during the first 30 s treatment at 300 W and 450 W, being log reductions lower than 0.5 log CFU g⁻¹. However, after 40 s treatment, log reductions had risen to 4.8 log CFU g⁻¹ at 800 W. Inactivation rates were higher at 600 W and 800 W (0.67 and 0.63 s⁻¹) than at 300 W and 450 W (<0.34 s⁻¹). The temperature-dependent parameters of a Weibull model obtained by Mattick, Legan, Humphrey & Peleg (2001) were evaluated. It was concluded that combinations characterized by a temperature equal or above 70 °C ensured a minimum 4 log reduction of Salmonella population (i.e. 300 W-80 s; 450 W-60 s or 600 W/800 W-40 s). These results may be of value in food service establishments, as target treatments for microwavable potato omelet portions.     

Comparison of composition, enzyme activity and selected functional properties of potato proteins isolated from potato juice with two different expanded bed resins

Protein concentrates prepared by expanded bed adsorption (EBA) chromatography from industrial potato juice (PJ) were analysed for chemical composition, color, enzyme activities, thermal properties and selected functional properties (solubility and emulsifying stability). Two EBA multi-modal resins, MIMO I-45 and MIMO 1300 (UpFront Chromatography), were employed under various pH conditions resulting in four potato protein concentrates, A-D. Concentrate B contained an electrophoretically pure protease inhibitor fraction (20-21 kDa), whereas concentrate A, C and D contained both patatin (41 kDa) and protease inhibitors. The potato protein concentrates were explored for the presence of transitions from native to denatured states using differential scanning calorimetry (DSC). Concentrate C had lower heat of transition (ΔH) and T-onset than the other concentrates. The concentrate containing protease inhibitors exhibited the highest denaturation temperature and enthalpy. All concentrates differed significantly (P < 0.05) in color brightness, with concentrate B and D emerging as the brightest. The solubility of the concentrates was evaluated at pH 6 and pH 4.5. All concentrates had lower solubility at pH 4.5 than at pH 6 (70-80%). The stability of emulsions (1% protein, 20% oil, 0.08% xanthan gum) against creaming was analysed with a new method based on the Single electrode Capacitance Probe (SeCaP) technology. Small differences among concentrates were observed by the new SeCaP method.     

Potato peel-based biopolymer film development using high-pressure homogenization, irradiation, and ultrasound

Edible films were developed from potato peel. High-pressure, gamma-ray, and ultrasound were applied to potato peel solutions to break down biopolymer particles in the solution small enough to allow for biopolymer film formation. Film properties, including moisture barrier and tensile properties, color, and microstructures, were investigated from the films formed with different concentrations of plasticizer (glycerol) and emulsifier (soy lecithin). High-pressure homogenization (HPH) produced the best films among the treatments at the conditions used in this research. Water vapor permeability (WVP) of films decreased by 32% with decrease in the concentrations of glycerol and soy lecithin by 40 and 75%, respectively. As the concentration of glycerol or soy lecithin increased, tensile strength of the films decreased up to 71%, but the elongation at break increased up to 161%, demonstrating lubricant effects of glycerol and soy lecithin. The lightness and yellowness of the films increased and the redness decreased with increase in the concentration of glycerol or soy lecithin. The concentrations of glycerol and soy lecithin were identified as important variables in producing biopolymer films from potato peel.     

Pasting properties of hydroxypropylated starches before or after proteinase treatment

To examine the effect of starch protein on hydroxypropylation, corn (normal and waxy) and potato starches were hydroxypropylated with propylene oxide at two levels (8.3 and 12.3% based on dry basis of starch weight) before or after proteinase (thermolysin) treatment, and then pasting properties of the starches were measured. For normal corn starch, protein appeared to be involved in hydroxypropylation, especially at the higher concentration of reagent (12.3%); the starch hydroxypropylated after proteinase treatment (Enz‐HP) showed less reaction efficiency than that only hydroxypropylated (HP) or proteinase treated starch after hydroxypropylation (HP‐Enz). This suggests a possible reaction between some of the reagent and the starch proteins that exist in the channel and surface of the starch granules. However, not much difference was found with the waxy corn starch, as it contains much lower amounts of amylose and protein than normal corn starch. The potato starch, which has no channels, showed complicated protein effects. For potato starch, a different access of the enzyme and chemical reagents to the granule matrix could be possible.     

Process‐product studies on starch acetylation reactions in pressurised carbon dioxide

An in‐depth study on the effect of process conditions (pressure, temperature and type of catalyst) on the acetylation of starch with acetic anhydride in pressurised carbon dioxide is described. A total of 22 experiments were performed and the experimental data were analysed using non‐linear multivariable regression. The highest degree of substitution (DS) value (0.46) was obtained using K₂CO₃ as the catalyst at 90°C, 15 MPa pressure, and a catalyst to starch ratio of 0.5 mol/mol anhydroglucose units (AGUs). Important product properties of the acetylated starch prepared in CO₂ like viscosity in water and relevant thermal properties were determined and compared with typical products prepared in an aqueous system.