Nutritional improvement of plant foods by non-thermal processing

Enhancing the washing of harvested quinoa seeds with ultrasound-assisted hydration

To improve the efficiency of harvested quinoa seed wash processing, this study comparatively evaluated the effects of ultrasound-assisted hydration (UH) and conventional hydration (CH) on hydration dynamics, saponin mass transfer kinetics, and pericarp structural changes in quinoa seeds. Moisture uptake was monitored using a gravimetric method, saponin content was determined through enzyme-linked immunosorbent assay, and pericarp structural changes were observed via scanning electron microscopy. The results showed that UH significantly enhanced the water absorption rate of quinoa seeds, with the Peleg model effectively fitting all hydration stages (R2 > 0.93). The saponin content in the seeds decreased rapidly at first and then stabilized, with the most significant reduction occurring within the first 30 min of soaking. UH reduced the saponin content by 52 %-73 %, outperforming CH, which reduced it by 42 %-53 %. Fick's diffusion model indicated that UH significantly increased the effective diffusion coefficient (Deff) of saponins and reduced the activation energy (Ea from 21.83 to 18.15 kJ/mol). SEM images confirmed that UH accelerated the rupture and pore formation of the pericarp. All kinetic models showed good fitting performance, with the Weibull and two-term models providing the best fit under both CH and UH conditions, evidenced by the highest R2 and lowest SSE, RMSE, and χ2 values. These findings contribute to optimizing industrial quinoa processing, enhancing efficiency and sustainability, and provide valuable guidance for the application of ultrasound technology in grain-based food development.

Beyond ultra-processed: considering the future role of food processing in human health

Food-based dietary guidelines have been the basis of public health recommendations for over half a century, but more recently, there has been a trend to classify the health properties of food not by its nutrient composition, but by the degree to which it has been processed. This concept has been supported by many association studies, narrative reviews and the findings from one randomised controlled feeding trial, which demonstrated the sustained effect of ultra-processed diets on increasing both energy intake and body weight. This has led to widespread speculation as to specific features of ultra-processed foods that promote increased energy intakes. Rising interest in the ultra-processed topic has led to proposals to include guidance and restrictions on the consumption of processed foods in national dietary guidelines, with some countries encouraging consumers to avoid highly processed foods completely, and only choose minimally processed foods. However, there remains a lack of consensus on the role of processed foods in human health when faced with the challenges of securing the food supply for a growing global population, that is, healthy, affordable and sustainable. There has also been criticism of the subjective nature of definitions used to differentiate foods by their degree of processing, and there is currently a lack of empirical data to support a clear mechanism by which highly processed foods promote greater energy intakes. Recommendations to avoid all highly processed foods are potentially harmful if they remove affordable sources of nutrients and will be impractical for most when an estimated two-thirds of current energy purchased are from processed or ultra-processed foods. The current review highlights some considerations when interpreting the dietary association studies that link processed food intake to health and offers a critique on some of the mechanisms proposed to explain the link between ultra-processed food and poor health. Recent research suggests a combination of higher energy density and faster meal eating rates are likely to influence meal size and energy intakes from processed foods and offers new perspectives on how to manage this in the future. In going beyond the ultra-processed debate, the aim is to summarise some important considerations when interpreting existing data and identify the important gaps for future research on the role of processed food in health.

Positive effects and mechanism of ultrasound on chitin preparation from shrimp shells by co-fermentation

The objective of this study is to explore the effect and mechanism of ultrasound on chitin extraction from shrimp shells powder (SSP) by the co-fermentation of Bacillus subtilis and Acetobacter pasteurianus. After pre-treating the SSP with high-intensity ultrasound (HIU) at 800 W, the protease activity in the fermentation solution reached 96.9 U/mL on day 3, which was significantly higher than for SSP that had not been pre-treated with ultrasound (81.8 U/mL). The fermentation time of the chitin extraction process was 5.0 d without ultrasound pre-treatment, while it was shortened to 4.5 d when using ultrasound at 800 W to treat SSP. However, there were no obvious differences when we applied ultrasound at low power (200 W, 400 W). Furthermore, chitin purified from shrimp shells pre-treated with HIU at 800 W exhibited lower molecular weight (11.2 kDa), higher chitin purity (89.8%), and a higher degree of deacetylation (21.1%) compared to SSP with no ultrasound pre-treatment (13.5 kDa, 86.6%, 18.5%). Results indicate that HIU peels off the protein/CaCO₃ matrix that covers the SSP surface. About 9.1% of protein and 4.7% of Ca²⁺ were released from SSP pre-treated with HIU at 800 W. These figures were both higher than with no ultrasound pre-treatment (4.5%, 3.2%). Additionally, the amount of soluble protein extracted from SSP through HIU at 800 W was 50% higher than for the control sample. SDS-PAGE analysis indicated that the soluble protein was degraded to the micromolecule. It also revealed that HIU (600, 800 W) induced the secondary and tertiary structure destruction of protein extracted from SSP. In conclusion, HIU-induced degradation and structural damage of protein enhances the protein/CaCO₃ matrix to be peeled off from SSP. Also, in the co-fermentation process, an increase of protease activity further accelerates deproteinization.

Effects of Pulsed Electric Fields and Ultrasound Processing on Proteins and Enzymes: A Review

There is increasing demand among consumers for food products free of chemical preservatives, minimally processed and have fresh-like natural flavors. To meet these growing demands, the industries and researchers are finding alternative processing methods, which involve nonthermal methods to obtain a quality product that meets the consumer demands and adheres to the food safety protocols. In the past two decades’ various research groups have developed a wide range of nonthermal processing methods, of which few have shown potential in replacing the traditional thermal processing systems. Among all the methods, ultrasonication (US) and pulsed electric field (PEF) seem to be the most effective in attaining desirable food products. Several researchers have shown that these methods significantly affect various major and minor nutritional components present in food, including proteins and enzymes. In this review, we are going to discuss the effect of nonthermal methods on proteins, including enzymes. This review comprises results from the latest studies conducted from all over the world, which would help the research community and industry investigate the future pathway for nonthermal processing methods, especially in preserving the nutritional safety and integrity of the food.

Green Extraction by Ultrasound, Microencapsulation by Spray Drying and Antioxidant Activity of the Tucuma Coproduct (Astrocaryum vulgare Mart.) Almonds

The industrial processing amazon fruits, like tucuma, generates a large amount of coproducts with large nutritional potential. Thus, this work obtained the oily extract of the tucuma almonds coproducts by green extraction using palm oil by the ultrasound method and then microencapsulated by atomization and verification of its antioxidant activity. Thermogravimetric techniques, infrared spectroscopy, scanning electron microscopy, moisture content, water activity were applied to characterize the microparticles. Total carotenoids were determined by UV spectroscopy and antioxidant activity was measured by 2,2′-azino-di-(3-ethylbenzthiazoline sulfonic acid and co-oxidation in the system β-carotene/linoleic acid. The oily extract and microparticle had total carotenoid contents of 3.305 mg/100 g ± 0.01 and 2.559 mg/100 g ± 0.01, respectively. The antioxidant activity assessed through the 2,2′-azino-di-(3-ethylbenzthiazoline sulfonic acid value was 584.75 μM/trolox ± 0.01 (oily extract) and 537.12 μM/trolox ± 0.01 (microparticle) were determined. In the system β-carotene/linoleic acid showed oxidation of 49.9% ± 1.8 lipophilic extract and 43.3% ± 2.3 microparticle. The results showed that the oily extract of the tucuma almond coproduct can be used as a carotenoid-rich source and microencapsuled with possible application for functional foods production.

Green and Non-conventional Extraction of Bioactive Compounds from Olive Leaves: Screening of Novel Natural Deep Eutectic Solvents and Investigation of Process Parameters

ABSTRACT

Olive leaf as an agricultural waste contains valuable bioactive compounds that are mainly used for pharmaceutical and cosmetic industries. Lately the major component, oleuropein, has gained extra attention due to the anti-viral activity against SARS-CoV-2 that causes Coronavirus disease (Covid-19). In this study, extraction of the bioactive compounds from olive leaves was conducted using a non-conventional and green method. New generation green solvents, natural deep eutectic solvents (NADES) were used in combination with ultrasound assisted extraction. Screening of NADES type, temperature, and particle size were investigated using one-pot-at-a-time method while, NADES amount and liquid-to-solid ratio were optimized using experimental design. The results were evaluated in terms of total polyphenol yield (Y_TP), total flavonoid yield (Y_TF) and antiradical activity (A_AR). At the optimized conditions, the highest total polyphenol yield and the highest total flavonoid yield were achieved with choline chloride-fructose-water (CFW) (5:2:5) as 187.31 ± 10.3 mg gallic acid equivalent g^-1 dw and 12.75 ± 0.6 mg apigenin equivalent g^-1 dw, respectively. The extracts were also analyzed for oleuropein, caffeic acid and luteolin contents. The highest amount of oleuropein and caffeic acid were extracted by glucose-fructose-water (GFW) (1:1:11) as 1630.80 mg kg^-1 dw and 112.77 mg kg^-1 dw, respectively.

SUPPLEMENTARY INFORMATION

The online version of this article (10.1007/s12649-021-01411-3) contains supplementary material, which is available to authorized users.

Comparative Evaluation of Four Extraction Methods of Antioxidant Compounds from Decatropis bicolor in Aqueous Medium Applying Response Surface Design

The objective of this paper is to compare conventional, ultrasound, microwave, and French press methods for the extraction of antioxidant compounds from Decatropis bicolor in an aqueous medium. This plant is widely used in Mexican traditional medicine for breast cancer treatment. Despite that, there are few studies on D. bicolor. Two response surface designs were applied to establish the best conditions of the liberation of antioxidants from D. bicolor, which were determined by DPPH• and Ferric Reducing Antioxidant Power (FRAP) techniques. The total phenolic content was evaluated by the Folin-Ciocalteu method. The results showed that D. bicolor is a source of antioxidants (669–2128 mg ET/100 g and 553–1920 mg EFe²⁺/100 g, respectively) and phenolic compounds (2232–9929 mg EGA/100 g). Among the physical factors that were analyzed, the temperature was the determinant factor to liberate the compounds of interest by using low concentrations of the sample and short times of extraction. The French press was the most efficient method, obtaining values of antioxidant activity and phenolic compounds even higher than those reported by using extraction methods with solvents such as methanol.

Field pea protein isolate/chitosan complex coacervates: Formation and characterization

Influence of chitosan (Ch) with low, medium, and high molecular weight (LMW, MMW, and HMW) on the formation of field pea protein isolate (FPPI)/Ch complex coacervates was investigated. An increase in maximum turbidity and a gradual shift of critical pH values towards the isoelectronic point of FPPI were observed as the FPPI/Ch ratio increased. Formation of FPPI/Ch complex coacervates was dominated by the electrostatic and hydrophobic interactions. FPPI/Ch complex coacervates exhibited a porous network microstructure and relatively uniform-sized and even-distributed pores were found in FPPI/Ch-HMW coacervates. Different thermodynamic profiles were observed during complex coacervation between FPPI and Ch with varying MWs and the largest binding stoichiometry was observed in the Ch-MMW at pH 6.6. In summary, the Ch-HMW was demonstrated to be most suitable for the formation of FPPI/Ch complex coacervates with homogenous microstructure but caused less changes in the tertiary conformation of FPPI compared to the Ch-LWM and Ch-MMW.

Production of triterpenoid compounds from Ganoderma lucidum spore powder using ultrasound-assisted extraction

When ingested as a dietary supplement, Ganoderma lucidum spore powders (GLSP) provide various health benefits such as enhanced immunity, liver protection and anti-cancer effects. In this study, triterpenoid extraction from GLSP was achieved using an ultrasound-assisted process which was optimized using response surface methodology (RSM). Ultrasound-assisted extraction (UAE) was also compared to the most conventional chemical extraction method. For UAE, optimum extraction conditions were found to be ethanol concentration = 95% v/v; solvent to solid ratio = 50:1 mL/g; ultrasound time = 5.4 min; ultrasound power = 564.7 w, and ultrasound probe distance = 8.2 cm. At optimal UAE conditions, no significant differences were found between experimental (0.97 ± 0.04 %) and predicted values (99%); which indicates appreciable correlation at the 97% confidence interval. The findings show the application of Box-Behnken design (BBD) to predict and optimize triterpenoid yield for UAE of triterpenoid from GLSP. Furthermore, glucose consumption was 2.68 times that of control samples when tested with insulin-resistant HepG2 cell, showing potential use in type 2 diabetes. In addition, triterpenoid extracts show good biocompatibility and inhibition of antioxidant activity.

Optimization of Ultrasound-Assisted Extraction of Antioxidant Polyphenols from the Seed Coats of Red Sword Bean (Canavalia gladiate (Jacq.) DC.)

The seed coat of red sword bean (Canavalia gladiata (Jacq.) DC.) is rich in antioxidant polyphenols. It is often discarded as a byproduct with the consumption of red sword bean, since it is very thick and not consumed by people. The aim of this study was to develop an ultrasound-assisted extraction method to extract natural antioxidants from the seed coats. The extraction process was optimized by using response surface methodology. After the single-factor experiments, three key factors, including ethanol concentration, liquid/solid ratio, and extraction time, were selected and their interactions were studied using a central composite design. The optimal extraction condition was 60.2% hydroethanol, a liquid/solid ratio of 29.3 mL/g, an extraction time of 18.4 min, an extraction temperature of 50 °C, and ultrasound power of 400 W. Under the optimal conditions, antioxidant activity of the extract was 755.98 ± 10.23 μmol Trolox/g dry weight (DW), much higher than that from maceration (558.77 ± 14.42 μmol Trolox/g DW) or Soxhlet extraction (479.81 ± 12.75 μmol Trolox/g DW). In addition, the main antioxidant compounds in the extract were identified and quantified by high-performance liquid chromatography–diode array detection–tandem mass spectrometry (HPLC–DAD–MS/MS). The concentrations of digalloyl hexoside, methyl gallate, gallic acid, trigalloyl hexoside, and digallic acid were 15.30 ± 0.98, 8.85 ± 0.51, 8.76 ± 0.36, 4.27 ± 0.21, and 2.89 ± 0.13 mg/g DW. This study provides an efficient and green extraction method for the extraction of natural antioxidants from the bean coat of red sword bean. The extract of antioxidants might be added into functional foods or nutraceuticals with potential beneficial functions.

Effect of Soluble Solids and High Pressure Treatment on Rheological Properties of Protein Enriched Mango Puree

The effects of high pressure treatment on the rheological properties of protein enriched mango puree were evaluated. In the first part, the original soluble solids in mango puree (28° Brix) was lowered to 26, 23 and 20° Brix, and each was supplemented with 2, 5 and 8% of whey protein to assess the influence of added protein. The samples were then evaluated by dynamic rheology. Pressure treatment resulted in a progressive increase in elastic (G') and viscous modulii (G″) as well as complex viscosity (η*). Values of G' were higher than G″ demonstrating that the product behaved more like a gel. Additional tests were carried out by simultaneously varying protein and soluble solids contents, and keeping the total solids at 28%. In this case, the effects of pressure levels and holding times were similar to previous results. However, the positive effects of higher protein were negated by the negative effects of lower soluble solids, resulting in an overall decreasing effect on rheology. The developed models effectively predicted the combined influence of protein and soluble solid concentrations on rheological parameters (R2 > 0.85). Sensory evaluation of 2% and 5% protein supplemented and pressure treated (500 MPa/3 min) mango puree yielded acceptable sensory qualities, resulting in a product with enriched protein content.

Impact of Pulsed Electric Fields on the Volatile Compounds Produced in Whole Onions (Allium cepa and Allium fistulosum)

The objective of this research was to investigate the effect of pulsed electric field (PEF) processing on the volatile compounds produced in onion cultivars. The changes in the volatile compounds of onions were assessed comparing results observed while measured immediately and 24 h after PEF treatment using headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). Significant increases in the concentrations of propanethial S-oxide, propenyl propyl thiosulfinate, 2-methyl-2-pentenal, dipropyl disulfide, propenyl propyl disulfide, methyl propyl disulfide, and methyl propenyl disulfide were observed immediately after PEF treatment. The concentrations of propenyl propyl thiosulfinate, dipropyl disulfide, methyl propyl disulfide, dipropyl trisulfide, methyl propyl trisulfide, and propenyl propyl trisulfide increased after 24 h compared to initial concentrations. It is postulated that these changes are due to PEF-induced cell permeabilisation that facilitates enzyme-substrate reactions after the PEF treatment.

Synergistic combinations of short high-voltage pulses and long low-voltage pulses enhance irreversible electroporation efficacy

Irreversible electroporation (IRE) uses ~100 μs pulsed electric fields to disrupt cell membranes for solid tumor ablation. Although IRE has achieved exciting preliminary clinical results, implementing IRE could be challenging because of volumetric limitations at the ablation region. Combining short high-voltage (SHV: 1600V, 2 μs, 1 Hz, 20 pulses) pulses with long low-voltage (LLV: 240-480 V, 100 μs, 1 Hz, 60-80 pulses) pulses induces a synergistic effect that enhances IRE efficacy. Here, cell cytotoxicity and tissue ablation were investigated. The results show that combining SHV pulses with LLV pulses induced SKOV3 cell death more effectively, and compared to either SHV pulses or LLV pulses applied alone, the combination significantly enhanced the ablation region. Particularly, prolonging the lag time (100 s) between SHV and LLV pulses further reduced cell viability and enhanced the ablation area. However, the sequence of SHV and LLV pulses was important, and the LLV + SHV combination was not as effective as the SHV + LLV combination. We offer a hypothesis to explain the synergistic effect behind enhanced cell cytotoxicity and enlarged ablation area. This work shows that combining SHV pulses with LLV pulses could be used as a focal therapy and merits investigation in larger pre-clinical models and microscopic mechanisms.

The influence of ultrasonic treatment on the growth of the strains of Salmonella enterica subs. typhimurium

This study proposes the destruction of pathogenic bacteria with the use of ultrasound waves because the more commonly used thermal processing methods often result in lowering the nutritional value of food. The study presents the impact of ultrasound of 20, 40 and 100 kHz frequencies and the power of 10.5 W/cm2 on the growth of the strain of Salmonella enterica subs. typhimurium. The tests were carried out both in chilled and non-chilled treatment mediums, with an average bacterial population >105 and >108 CFU/cm3. The total inactivation of Salmonella spp. was observed in the tests in the low-population non-chilled treatment medium after sonication at 20 and 40 kHz for 30 min, and in high bacterial population at 20 kHz for 30 min. A reduction in the average number of bacteria was reported in the low-population non-chilled medium after 15 min of sonication at 20, 40 and 100 kHz; after 15 min of sonication at 20 and 100 kHz of the material of high bacterial population; and in the low-population chilled treatment mediums after 15 and 30 min at 20 kHz. The samples with inactivated bacteria and those with reduced bacterial counts maintained the same levels when stored at 4 °C for 24 and 48 h. Bacteria inactivation obtained after sonication lasted for up to 48 h in storage at 21 °C. For the samples with reduced bacterial counts stored at 21 °C, a rise in the average number of bacteria was recorded.

Irreversible electroporation ablation area enhanced by synergistic high- and low-voltage pulses

Irreversible electroporation (IRE) produced by a pulsed electric field can ablate tissue. In this study, we achieved an enhancement in ablation area by using a combination of short high-voltage pulses (HVPs) to create a large electroporated area and long low-voltage pulses (LVPs) to ablate the electroporated area. The experiments were conducted in potato tuber slices. Slices were ablated with an array of four pairs of parallel steel electrodes using one of the following four electric pulse protocols: HVP, LVP, synergistic HVP+LVP (SHLVP) or LVP+HVP. Our results showed that the SHLVPs more effectively necrotized tissue than either the HVPs or LVPs, even when the SHLVP dose was the same as or lower than the HVP or LVP doses. The HVP and LVP order mattered and only HVPs+LVPs (SHLVPs) treatments increased the size of the ablation zone because the HVPs created a large electroporated area that was more susceptible to the subsequent LVPs. Real-time temperature change monitoring confirmed that the tissue was non-thermally ablated by the electric pulses. Theoretical calculations of the synergistic effects of the SHLVPs on tissue ablation were performed. Our proposed SHLVP protocol provides options for tissue ablation and may be applied to optimize the current clinical IRE protocols.

Green ultrasound-assisted extraction of carotenoids from pomegranate wastes using vegetable oils

The objective of this work was to develop a new process for pomegranate peels application in food industries based on ultrasound-assisted extraction of carotenoids using different vegetable oils as solvents. In this way, an oil enriched with antioxidants is produced. Sunflower oil and soy oil were used as alternative solvents and the effects of various parameters on extraction yield were studied. Extraction temperature, solid/oil ratio, amplitude level, and extraction time were the factors investigated with respect to extraction yield. Comparative studies between ultrasound-assisted and conventional solvent extraction were carried out in terms of processing procedure and total carotenoids content. The efficient extraction period for achieving maximum yield of pomegranate peel carotenoids was about 30min. The optimum operating conditions were found to be: extraction temperature, 51.5°C; peels/solvent ratio, 0.10; amplitude level, 58.8%; solvent, sunflower oil. A second-order kinetic model was successfully developed for describing the mechanism of ultrasound extraction under different processing parameters.

The role of additional pulses in electropermeabilization protocols

Electropermeabilization (EP) based protocols such as those applied in medicine, food processing or environmental management, are well established and widely used. The applied voltage, as well as tissue electric conductivity, are of utmost importance for assessing final electropermeabilized area and thus EP effectiveness. Experimental results from literature report that, under certain EP protocols, consecutive pulses increase tissue electric conductivity and even the permeabilization amount. Here we introduce a theoretical model that takes into account this effect in the application of an EP-based protocol, and its validation with experimental measurements. The theoretical model describes the electric field distribution by a nonlinear Laplace equation with a variable conductivity coefficient depending on the electric field, the temperature and the quantity of pulses, and the Penne's Bioheat equation for temperature variations. In the experiments, a vegetable tissue model (potato slice) is used for measuring electric currents and tissue electropermeabilized area in different EP protocols. Experimental measurements show that, during sequential pulses and keeping constant the applied voltage, the electric current density and the blackened (electropermeabilized) area increase. This behavior can only be attributed to a rise in the electric conductivity due to a higher number of pulses. Accordingly, we present a theoretical modeling of an EP protocol that predicts correctly the increment in the electric current density observed experimentally during the addition of pulses. The model also demonstrates that the electric current increase is due to a rise in the electric conductivity, in turn induced by temperature and pulse number, with no significant changes in the electric field distribution. The EP model introduced, based on a novel formulation of the electric conductivity, leads to a more realistic description of the EP phenomenon, hopefully providing more accurate predictions of treatment outcomes.

Optimisation of ultrasound-assisted extraction of oil from papaya seed by response surface methodology: oil recovery, radical scavenging antioxidant activity, and oxidation stability

The present study aimed to investigate the effects of ultrasound-assisted extraction (UAE) condition on the yield, antioxidant activity and stability of the oil from papaya seed. The studied ultrasound variables were time, temperature, ultrasound power and solvent to sample ratio. The main goal was to optimise UAE condition providing the highest recovery of papaya seed oil with the most desirable antioxidant activity and stability. The interaction of ultrasound variables had the most and least significant effects on the antioxidant activity and stability, respectively. Ultrasound-assisted extraction provided a relatively high oil recovery (∼ 73%) from papaya seed. The strongest antioxidant activity was achieved by the extraction at the elevated temperature using low solvent to sample ratio. The optimum ultrasound extraction was set at the elevated temperature (62.5 °C) for 38.5 min at high ultrasound power (700 W) using medium solvent to sample ratio (∼ 7:1 v/w). The optimum point was practically validated.

Effect of ultrasonic treatment on the polyphenol content and antioxidant capacity of extract from defatted hemp, flax and canola seed cakes

The effectiveness of ultrasonic extraction of phenolics and flavonoids from defatted hemp, flax and canola seed cakes was compared to the conventional extraction method. Ultrasonic treatment at room temperature showed increased polyphenol extraction yield and antioxidant capacity by two-fold over the conventional extraction method. Different combinations of ultrasonic treatment parameters consisting of solvent volume (25, 50, 75 and 100 mL), extraction time (20, 30 and 40 min) and temperature (40, 50, 60 and 70 °C) were selected for polyphenol extractions from the seed cakes. The chosen parameters had a significant effect (p<0.05) on the polyphenol extraction yield and subsequent antioxidant capacity from the seed cakes. Application of heat during ultrasonic extraction yielded higher polyphenol content in extracts compared to the non-heated extraction. From an orthogonal design test, the best combination of parameters was 50 mL of solvent volume, 20 min of extraction time and 70 °C of ultrasonic temperature.

Physical barriers to carotenoid bioaccessibility. Ultrastructure survey of chromoplast and cell wall morphology in nine carotenoid-containing fruits and vegetables

BACKGROUND

The ultrastructural characterisation of cellular components is a key element in revealing the bases for differences in nutrient bioaccessibility among fruits and vegetables and their derived products. Together, cell walls and chromoplasts constitute the two major physical barriers to carotenoid release from the food matrix (structure) during digestion. In general, larger cells with thinner cell walls are most likely to fail under mechanical pressure. In relation to chromoplasts, the substructures plastoglobuli, crystals and membranes give decreasing rates of carotenoid solubilisation when exposed to digestive forces.

RESULTS

This paper describes cell wall and chromoplast structures in nine carotenoid-storing raw fruits and vegetables. Watermelon and melon cells were shown to have the largest cells concomitant with thin, non-fibrous cell walls, while carrot, hypodermal grapefruit and sweet potato cells were smallest with fibrous or dense cell walls. Mango fruit showed the highest proportion of globules to other substructures. Carrot, papaya and tomato contained many crystalline structures. Finally, watermelon, mango and butternut squash developed a high proportion of membranous structures.

CONCLUSION

A more precise description of the physical characteristics of foods that stand as barriers to bioaccessibility can help in understanding which are more or less inhibitory for particular foods.