Fruit Slices Research Articles

Combined radio frequency-vacuum and hot air drying of kiwifruits: Effect on drying uniformity, energy efficiency and product quality

Two drying methods, both individually and in their combination [RF-vacuum drying (RFVD), hot air drying (HAD) and RFVD+HAD] were evaluated for three-layer drying of 6 mm thick kiwifruit slices in order to shorten drying time, improve energy efficiency and product quality. An electrode gap of 95 mm and vacuum of 20.1 kPa were selected for RFVD applications based on previous studies. Results showed that the total drying time was the shortest (480 min) when using RFVD, followed by RFVD+HAD (600 min; 20% longer) and HAD (900 min, almost double). However, non-uniform drying patterns were observed in both RFVD and HAD methods, but the RFVD+HAD process resulted in a more uniform moisture distribution both within and among the fruit slices. The average energy efficiency of HAD was improved remarkably from 9.92% to 22.93% by applying the RFVD+HAD method. Additionally, the RFVD+HAD process resulted in better product quality attributes like color, shrinkage ratio and rehydration capacity. Therefore, the RFVD+HAD method is recommended as a time and energy efficient drying technology for kiwifruits with a better moisture distribution and product quality. • Three methods were evaluated for drying uniformity, energy efficiency and product quality. • Combined RFVD+HAD process yielded more uniform moisture distribution in/among kiwifruit slices. • Final product dried by combined RFVD+HAD process had better quality attributes.

Shelf-Life of Pumpkin Fruit Slices, Flour and Blended Products

Pumpkin has high potential of generating income and overcoming food insecurity. Today’s consumer looks upon the food industry to provide healthy, attractive convenience products that remain wholesome for long. However, spoilage of horticultural produce results due to improper handling and microbial attack. Microbial spoilage is the major factor limiting shelf-life of fresh produce and processed products. It arises from improper handling and spore contamination, leading to economic loss. The objective of the present study was to determine whether shelf-life of value-added pumpkin products could be prolonged by wrapping, drying, or processing. The study used products in three experiments: (1) pumpkin fresh fruit (presented as whole, half slices or quarter slices plus or minus clear shrink wrap); (2) pure flour (dried using oven, enhanced solar, or open sun); and (3) bakery products (cake, cookies, scones, <i>mandazi</i>, bread, porridge, <i>chapatti or irio</i> blended with 0%, 5%, 20%, 50% or 90% pumpkin flour). All experiments were conducted in completely randomized design, replicated four times and repeated once. Pooled average data values were subjected to analysis of variance and significantly different means were separated using the least significantly difference test at α = 0.05. Plate Count Agar and Potato Dextrose Agar were used to determine total viable counts and fungi, respectively, on pumpkin fresh fruit, dried flour and blended products, while MacConkey Agar was used to assess enteric bacteria in dried flour and blended products. Results showed significant differences (<i>P</i><0.0001) in number of days taken for the tested samples to get spoilt. Slicing fruit drastically reduced shelf-life from 142 days to about 3 to 5 days. There were significant differences (<i>P</i><0.0001) in shelf-life of flour from the three drying methods. Enhanced solar dried flour had longest shelf-life of 11.5 months. Bacilli were the dominant bacteria in fresh fruit slices, while flour had bacilli and cocci, which were also dominant in blended products. Significant difference (<i>P</i><0.0001) occurred in moisture content of cake, <i>mandazi</i> and scones with various flour-blending levels. Cookies had the longest shelf-life of 64 days, while <i>irio</i>, <i>chapatti</i> and porridge got spoilt after two days. Significant differences occurred in microbial counts of the various flour-blended products throughout the storage periods. Baked products with up to 20% pumpkin flour-blend had great potential of remaining wholesome for longest storage period and hence are recommended for adoption.

Influence of Sulphite on the Drying Kinetics of Pumpkin Fruit Slices

Drying kinetics, of pumpkin fruit slices as influenced by sulphiting, was investigated. Pumpkin fruits, were sulphited at 0, 1.0, 1.5, 2.0 and 2.5% to obtain 4 mm thick (P0, 4; P1, 4; P1.5 4; P2, 4; P2.5, 4 - and 5 mm samples (P0, 5; P1, 5; P1.5, 5; P2, 5; P2.5, 5 respectively). Samples were dried at 60, 65, 70, 75 and 80°C at an air velocity of 1.53 m/s. Drying was carried out to constant moisture. Samples were screened using descriptive sensory evaluation to obtain samples P1, 4 and P2, 5 each dried at 75°C as the best samples for 4 mm and 5 mm respectively. Drying curves, moisture diffusitivity, activation energy, drying time and rehydration capacity were determined. The drying curves obtained showed results for a short constant rate followed by a falling rate period. The effective moisture diffusivity varied from 6.235×10^-11 to 12.808×10^-11m²/s for the 4 mm and 9.046 x 10-11 to 21.330 x 10^-11m²/s for the 5 mm samples. Activation energy obtained for P0, 4; P1, 4; P0, 5 and P2, 5 were 31.342, 32.292, 31.525 and 29.88 kJ/mol. respectively. Sulphiting reduced drying time at 1% level from 16.5 to 15.2 hours for the 4 mm sample and 17.8 to 16.9 hours at 2% level of sulphiting for the 5 mm. Sulphite treatment reduced rehydration capacity significantly at p>0.05. This study implies that the parameter which governed the internal transfer of moisture was moisture diffusion.

Processing and evaluation of osmodried mango slices – A micronutrient rich food

Osmotic dehydration is a novel technique for the production of shelf stable, nutritious and tasty products. Mango is a fruit which is highly relished in both raw and processed form. Various studies have indicated that pretreatment of fruits prior to osmotic dehydration improved the quality of the product. Hence, an attempt was made to study the effect of various pretreatments in the quality characteristics of osmo dried fruits. Two varieties of mango namely Bangalora and Pairi were selected for the study. The fruits were washed, peeled, destoned and cut to slices. The slices were given four pretreatments viz., soaking the fruit slices in a solution of citric acid, citric acid + KMS, ascorbic acid and ascorbic acid + KMS for 30 min. After pretreatment the fruit slices were soaked in the osmotic agent (sugar syrup) for 18 h followed by dehydration, cooling and packing. The dried fruit slices were packed in metallised polypropylene packs and subjected to shelf-life studies for a period of 180 days. Analysis of the physio-chemical qualities, microbial and sensory qualities of the fruit slices during storage, indicated that the osmo dried fruit samples pretreated with ascorbic acid +KMS and citric acid + KMS had retained highly acceptable qualities.

Investigation Effective Moisture Diffusivity and Activation Energy on Convective Hot Air Drying Assisted Extraction of Dragon Fruit Slices

Good drying system is evaluated by its efficiency in removing the moisture content of products to a certain level and at the same time decrease the quality degradation that occurs in drying process. The objective of this study was to investigation effective moisture diffusivity and activation energy on convective hot air drying assisted extraction of dragon fruit slices. Drying experiments were performed under 3 temperatures of 60, 70 and 80°C, air velocities of 1.0 m/s and two thickness of thin layer of 3 and 5 mm. Investigate the effect of drying conditions on drying kinetics and qualities attributes of dragon fruit slices, namely, antioxidant activity determined by DPPH methods and total color changes (ΔE) of dried dragon fruit slices. The results show that the drying time decreased with increased in drying temperature but increased with the decreasing of thin layer thickness. The highest effective moisture diffusivity thickness thin layer of 3 mm was found to be 3.55×10-9 m2/s and thickness thin layer of 5 mm was found to be 9.21×10-10 m2/s, effective moisture diffusivity increased with the temperature. An Arrhenius relation with an activation energy showed that a higher value of thickness of thin layer of 3 mm. The experimental results showed that higher drying temperature led to higher effective diffusion coefficient, antioxidant activity and total color changes.

Mass transfer modeling during osmotic dehydration of cambuci (Campomanesia phaea (O. Berg) Landrum) slices and quality assessment

The osmotic dehydration of cambuci slices was studied using binary and ternary solutions containing sorbitol (S) and calcium lactate (CL) at different concentrations. Experiments were conducted at 25 °C. The mass and the physical-chemical properties of fruit slices were measured along the process. The results showed significant reduction in moisture (X), water activity (aw) and titratable acidy (TA). Soluble solids (SS) and pH increase were also observed. Osmotic solutions with higher sorbitol concentrations enabled higher water removal, but no significant difference was observed when CL was added to the osmotic solution. The content of soluble solids (SS) was higher in samples treated with higher sorbitol concentrations. The experimental results of water loss and soluble solids gain were modeled using Peleg's equation, and the equilibrium moisture and content of soluble solids were estimated. The effective diffusion coefficient of water was lower when CL was added to the osmotic solution, indicating modifications in the internal resistance for the mass transfer.

Radio Frequency-Vacuum Drying of Kiwifruits: Kinetics, Uniformity, and Product Quality

To overcome long drying time, low energy efficiency and poor product quality associated with conventional drying, a radio frequency (RF) vacuum technology is proposed for drying kiwifruit slices using a 27.12 MHz, 3 kW RF-vacuum drying system. The results demonstrated that the process variables, electrode gap, vacuum pressure, and sample thickness, had major effects on the RF-vacuum drying. The RF-vacuum drying was associated with internal heating and rapid drying resulting in 65% reduction of hot air drying (60 °C) time. Moreover, kiwifruits dehydrated by RF-vacuum drying were associated with better color stability, higher vitamin C retention, and higher rehydration capacity (p < 0.05) as compared with hot-air-dried samples. Based on acceptable drying rate, stable temperature and avoiding arcing, a RF-vacuum drying protocol with the electrode gap of 60 mm, vacuum pressure of 0.02 MPa, and sample thickness of 8 mm was identified. Despite some differences observed in individual fruit slices, the RF-vacuum drying technique achieved better and more uniform drying patterns among the samples. Overall, the RF-vacuum drying process may provide a more effective and practical method for high-quality dehydration of kiwifruits.

The Effect of Sugar and Agar-agar Concentration on Nypa Fruit Slice Jam

Nypa fruticans or known as nypa produces considerable amount of fruit with high content of carbohydrate. The mesocarp of the mature fruit is a potential source of energy but underutilised. This research was conducted to study the production of nypa slice jam by focussing on the effect of sugar and agar-agar concentration on the physical, chemical and sensory properties of nypa slice jam. Sugar and agar-agar concentration affect rendemen, crude fibre content, total soluble solid, water content, colour, texture, taste, flavour and overal acceptance of slice jam from nypa fruit.

Extraction and characterization of natural enzymes from bottle gourd (Lagenaria siceraria) and effect of enzyme inhibitors in extending the shelf life of bottle gourd cut pieces

Fresh-cut fruits and vegetables are one of the widely consumed commodities in grocery stores. Fruits and vegetables on trimming lose their natural protection leading to browning and other undesirable changes. In this study, a novel method following minimal processing concept with hurdle technology was formulated to improve the shelf life of fresh-cut bottle gourd. Characterisation of the bottle gourd extract revealed the presence of indigenous enzymes xylanase, pectinase, and amylase. Since these enzymes cause spoilage, a pre-treatment of bottle gourd slices using different combinations of EDTA, CaCl2, sodium metabisulphite (SMS) and citric acid was studied to inhibit the enzyme activity. Pre-treatment using a combination of 1 mM EDTA, 2.5% CaCl2, 2% Sodium metabisulphite (SMS) and 0.5% Citric acid inhibited the enzymes efficiently. Further, to prevent the water leaching during storage, the fruit slices were fed to a partial dehydration (30%) process. The hurdle technology, chemical pre-treatment followed by partial dehydration, helped the cut-bottle gourd pieces to stay acceptable in terms of titrable acidity, total solids, texture, color, and microbial quality for 20 days at 4 °C.

Efficacy of Osmo-Convective Process Parameters for Kinnow Fruit Slices and Its Optimization Using Response Surface Methodology

The optimal condition for osmo-dehydrated kinnow product from kinnow fruit slices with peel by simultaneous osmo-convective dehydration was evaluated. The process parameters used for sugar osmosed samples were; osmotic process temperature (35–75 °C), solution concentration (55–75°Brix), immersion time (150–270 min) and convective drying temperature (45–65 °C). A Central Composite Rotatable Design was employed to assess the different Osmo-convective parameters. The optimized conditions for developed kinnow product were found to be osmotic process temperature 65 °C, convective drying temperature 50 °C, concentration 61°Brix and immersion time 187 min.

Quality, sensory and volatile profiles of fresh‐cut big top nectarines cold stored in air or modified atmosphere packaging

SummarySolid‐phase microextraction (SPME) GC‐MS was used to investigate the volatile organic compound (VOC) profile of fresh‐cut ‘Big Top’ nectarine samples, stored in unsealed bags (AIR) or packed in active modified atmosphere (MAP) after 8 days of cold storage. Nectarine slices were also subjected to sensory and quality analysis after harvest and at the end of the storage. MAP preserved the overall quality, the appearance and the olfactory properties of nectarine slices during storage, while AIR samples showed symptoms of dehydration and browning. Sixty VOCs were identified in total in the headspace of the fresh nectarines and cold‐stored fruit slices samples. Principal component analysis performed on VOCs allowed to differentiate fresh nectarines from cold‐stored samples, with lactones and terpenes mainly related to fresh samples, and ester compounds positively correlated to AIR or MAP samples. Partial least square regression models allowed to identify a pool of VOC predictors of olfactory sensory descriptors.

Insights in convective drying of fruit by coupled modeling of fruit drying, deformation, quality evolution and convective exchange with the airflow

Coupled modeling of fruit drying, deformation and quality evolution of a half-circular apple fruit slice is combined with modeling of the convective heat and mass exchange with the airflow. The aim was to gain more insight in the fruit drying kinetics, more particular in heterogeneities and couplings in moisture content and shrinkage as well as quality loss within the fruit during drying. Further aims were to investigate the impact of several modeling assumptions and to analyze the effect of the peel on the drying behavior. Large differences in internal moisture distribution and deformation were observed within the fruit slice. They were caused by the complex airflow field around the slice, which induced a spatial variation in convective heat/mass transfer coefficients (CTCs) over the fruit surface. The differences with imposing a single, constant CTC across the fruit surface (non-conjugate approach) indicated the need for including spatially-resolved CTCs (conjugate approach). The impact of including deformation in the model was also quantified. Not accounting for explicit airflow modeling or deformation affected the fruit temperature, and thereby also the fruit quality decay. The presence of a peel affected the drying process and the deformation, resulting in an asymmetrical collapse towards the center of the fruit slice. Coupling the modeled hygrothermal history of the fruit during drying, to fruit quality modeling opens new opportunities for optimizing drying processes. Thereby, the process can be optimized not only in terms of drying time or energy consumption, but also to achieve the best product quality.

Acrylamide in thermal-processed carbohydrate-rich foods from Chinese market

ABSTRACTAcrylamide content in food market in China was determined with the goal to evaluate related health concern. In this survey, products of rice, potato corn, wheat as well as dried fruit slices and instant foods were analysed. All these types of thermal-processed carbohydrate-rich foods were frequently consumed in China. They were purchased from markets in Zhejiang province and analysed using a liquid chromatography tandem/mass spectrometry method. Acrylamide was detected in 94.3% of 105 investigated samples, ranging from 10 to 3649 μg/kg with an average value of 231 μg/kg and a median of 114 μg/kg. In this study, high levels were found in potato products (564 ± 285 μg/kg), corn products (524 ± 187 μg/kg) and instant foods (180 ± 35 μg/kg) while low levels were measured in rice products (82 ± 17 μg/kg), wheat products (96 ± 29 μg/kg) and dried fruit slices (83 ± 13 μg/kg).

In Situ Raman Analysis of CO₂-Assisted Drying of Fruit-Slices.

This work explores the feasibility of applying in situ Raman spectroscopy for the online monitoring of the supercritical carbon dioxide (SC-CO2) drying of fruits. Specifically, we investigate two types of fruits: mango and persimmon. The drying experiments were carried out inside an optical accessible vessel at 10 MPa and 313 K. The Raman spectra reveal: (i) the reduction of the water from the fruit slice and (ii) the change of the fruit matrix structure during the drying process. Two different Raman excitation wavelengths were compared: 532 nm and 785 nm. With respect to the quality of the obtained spectra, the 532 nm excitation wavelength was superior due to a higher signal-to-noise ratio and due to a resonant excitation scheme of the carotenoid molecules. It was found that the absorption of CO2 into the fruit matrix enhances the extraction of water, which was expressed by the obtained drying kinetic curve.

Chemical evaluation of the Rhynchophorus ferrugineus larvae fed on different substrates as human food source.

We investigated the chemical composition of the weevil Rhynchophorus ferrugineus larvae, traditionally used as human food in Asia and known worldwide as one of the most significant pest for palm trees. Total fat content and fatty acid composition were analyzed using standard methodologies in (1) weevil larvae reared on apple fruit slices and wild specimens collected from attacked (2) Phoenix canariensis and (3) Syagrus romanzoffiana palm trees. Total fat content was extremely high in all the specimens (ranged between 57.62 and 60.03% based on dry weight). Despite sharing the same prevalent fatty acids (myristic acid, palmitic acid, stearic acid, palmitoleic acid, oleic acid, α-linoleic acid, and α-linolenic acid), fatty acid composition of the wild weevil larvae significantly differed from that of the specimens raised on apple fruit, due to the presence of other minor compounds. In general, a good balance between unsaturated fatty acids (∼53.68% of total fatty acids) and saturated fatty acids (∼43.41% of total fatty acids) and a low cholesterol content (74.61-152.32 mg/kg based on dry matter) were detected in all the specimens. Conversely, the weevil larvae did not represent a good source of α-tocopherol (14.17-26.22 mg/kg based on dry matter). The ability of the protein extracts obtained from the weevil larvae to inhibit invitro the angiotensin-converting enzyme, the main enzyme involved in blood pressure regulation, was also investigated. To simulate gastrointestinal digestion process, protein extracts were hydrolyzed by the gastrointestinal enzymes. A significantly lower IC50 (0.588-0.623 mg/ml) was measured in all the protein extracts after enzymatic hydrolysis versus the corresponding crude protein extracts (3.270-3.752 mg/ml). Given that the weevil larvae are able to provide interesting benefits for human health, this study supports their use as human food not just in the native countries where they are traditionally consumed and farmed but also throughout the world.

Chemical composition of apple fruit, juice and pomace and the correlation between phenolic content, enzymatic activity and browning

Primary and secondary metabolites were evaluated in apple fruit, juice and pomace of scab resistant and leading European apple cultivars. The primary goal was to study the chemical composition of apple fruit fractions in correlation with their enzymatic browning. Additional goal was to assess the suitability of apple pomace for the extraction of phenolic compounds. Furthermore, the cultivars were grouped according to their suitability for fresh-cut fruit slices by measuring their enzymatic activity, total phenolic content (TPC) and the rate of browning. Highest TPC was determined in ‘Granny Smith’ pomace suggesting its optimal suitability for phenolic extraction among the analyzed apple cultivars. ‘Majda’ fruit (investigated for the first time) can be offered to the market as fresh-cut slices as almost no changes in pulp color have been detected due to oxidation. The correlation test showed that oxidation of apple pulp is highly dependent on TPC and weakly correlated to the activity of polyphenol oxidase. Contrary, no significant correlation has been determined between the rate of oxidation and the activity of peroxidase.

Characterization of Myoviridae and Podoviridae family bacteriophages of Erwinia amylovora from Hungary - potential of application in biological control of fire blight

Twelve bacteriophage isolates of Erwinia amylovora, the causal agent of fire blight, were isolated from blighted apple, pear and quince trees from different sites in Hungary. According to morphological characteristics they were assigned to the order Caudovirales, two isolates belonging to the Podoviridae and ten to the Myoviridae families. Examining plaque morphology, host range and molecular characterization by PCR established that these phages are not identical neither to the three North American strains used as references nor the earlier isolated Hungarian Siphoviridae strains. Studying the efficacy of selected phages in apple blossoms and green pear fruit slices it was found that a combination of three phage isolates (ΦEaH2A, ΦEaH5K and ΦEaH7B) significantly reduced bacterial multiplication and fire blight symptoms as compared to untreated controls. Combined application of these new E. amylovora-specific phages as biocontrol agents may contribute to a better control of E. amylovora under field conditions.

Impact of size and shape of fresh-cut fruit on the drying time and fruit quality

Insights are provided on how fruit size and shape affect the drying time and fruit quality loss, by simulating the convective drying process for cubic, rectangular, circular and half-circular fruit slices. Combined hygrothermal-quality modelling of the drying process unveiled, quantitatively, to which extent smaller samples dry faster and retain their quality better. For rectangular pieces with a large aspect ratio, so called fruit sticks, the drying time did not change anymore for increasing length. The compactness is proposed as a parameter to compare the drying process of fruits with different sizes and shapes with one another. The compactness is the ratio of the fruit volume to the surface area exposed to the environment. A good correlation function was found of both drying time and quality loss with the fruit compactness, where fruit with a lower compactness clearly dry faster. Such correlations can aid in estimating a-priori the drying time for a fruit of a certain size and shape.

Quality comparison of dried slices processed from whole persimmons treated with different deastringency methods.

The effects of different deastringency treatments (untreated, carbon dioxide, warm water, or ethanol), before drying on the quality characteristics of dried fruit slices prepared from whole "Cheongdobansi" persimmons were evaluated. L* (lightness) and a* (redness) values of dried slices from warm water- and ethanol-treated groups were higher, respectively, compared to that of dried slices from other groups. Hardness was lower in dried slices from ethanol-treated fruits. Moisture, water activity, soluble solids, titratable acidity, and sensory properties (color, aroma, texture, sweetness, and overall acceptability) of the dried slices from astringency-removed fruits were higher when compared to those of the dried slices from non-treated persimmons. In particular, the dried slices from ethanol-treated fruits showed the highest values for these parameters. Moreover, soluble tannin and DPPH radical scavenging activity decreased by deastringency treatment. Results suggest that ethanol deastringency treatment before drying could be a useful method to improve most quality characteristics, except antioxidative activity, of dried persimmon slices.

The Effect of the Drying Method on the Quality of Dried Kiwi Slices

Abstract— Drying is known as a food preservation method which increases the food’s storage time by water reduction. Traditional drying consisted of open sun-drying, but different industrial dryers have been widely used in recent times. The new dryers consist of convective, infrared, ultrasound, freeze fluidized bed and freeze dryers. All of these dryers reduce the water content but under different mechanisms which leads to the end products with different qualities. In this study we aim to compare the difference in quality of kiwi fruit slices dried by three different dryers: 1. Convective tray dryer, 2. Microwave dryer and 3. Freeze dryer. The tray dryer experiments were conducted in two air temperatures of 60 and 80oC in the constant air velocity of 0.8 m/s. The microwave dryer operated in 3 output powers of 180, 270 and 360 W. The condenser temperature and pressure in the freeze dryer reduced to -50oC and 0.1 mbar, respectively. The operating conditions and time were regulated so that the moisture content of all dried samples reduced to nearly 10% in the wet basis. The three parameters of color change, ascorbic acid and antioxidant reduction were selected as the measuring criteria for the comparison of the product qualities. The experiments show that the freeze drying caused the minimum color change while the microwave drying in the maximum power of 360W caused the maximum amount of color change. The concentration of ascorbic acid was measured in the fresh fruits and dried samples by standard methods. The measurements proved that the ascorbic acid content of the freeze dried samples was 80% of the fresh fruits. The ascorbic acid content of other samples was much lower. The antioxidant activity of the dried samples and the fresh fruits was also measured by standard methods and the experimental data also showed that the freeze drying causes the minimum reduction in the antioxidant activity.