Application of non-thermal pretreatment techniques on agricultural products prior to drying: a review.

BACKGROUND: Most agricultural crops contain high moisture content (80-95% wet basis (wb)) which makes them very susceptible to microbial damage leading to shorter shelf-life and high postharvest losses. The high perishability of these agricultural products requires preservation techniques to prolong their shelf-lives. Drying remains an important component of processing in this regard. Therefore, any pretreatment methods for drying agricultural product that decreases the moisture content and minimizes drying time by conserving the quality of the crop product is of prime significance. This article is a comprehensive review of recent developments of non-thermal pretreatment (NTP) methods. A summary of their significance, emerging and innovative methods of this technology together with its applications and limitations are discussed. This article further examines the environmental impact of NTP techniques. RESULTS: NTP techniques, such as high pressure, ultrasound, pulsed electric field and osmotic dehydration methods are essential operations for pre-dehydration of agricultural products prior to drying. These techniques can avoid the deleterious effects of heat on nutritive value, colour and flavour of agricultural products compared to thermal pretreatments. They also enhance the inactivation of the enzymes, improve energy efficiency and mass transfer, reduce processing time, preserve bioactive compounds, improve drying kinetics and drying rate, minimize enzymatic browning, and enhance product quality. CONCLUSION: These findings will provide a better understanding of different NTP methods and also make available more information for selecting pretreatment techniques for drying of agricultural products. © 2020 Society of Chemical Industry.

Variation in bioactive phytochemicals and sensory attributes of osmosonic convective dried ginger from four African countries.

BACKGROUND: The rhizome of ginger (Zingiber officinale Roscoe) is one of the most patronized spices worldwide and plays an important role in folklore medicine. In this study, we aimed to determine the quality of ginger samples from representative West African (Ghana, Nigeria) and East African (Uganda, Kenya) countries. By that, we also implicitly sought to determine the probable influence of location of cultivation (and the intrinsic growth conditions) on the quality of the samples. The ginger samples were pretreated by osmosonication prior to relative humidity convective drying and analyzed for differences in their metabolomes, total phenolic content (TPC) and total flavonoid content (TFC), antioxidant activities, sensory characteristics and volatile compounds composition (via electronic-nose determination). RESULTS: The outcome of our study showed marked source-dependent differences in the metabolomes of the samples as captured by a metabolomics approach. Based on the findings of the metabolomics study, 6-gingerol content was quantified and found to be higher in the samples of West African origin. Also, the samples from the two West African countries contained higher levels of bioactive phytochemicals as evinced by the results of TPC, TFC, e-nose analysis, and antioxidant activities. They also gave better sensory attributes. CONCLUSION: In summary, for all parameters assessed, and on a country-by-country basis, the general quality trend observed was: Ghana > Nigeria > Uganda > Kenya. All results taken together, our findings at least in part, point to the influence of geographical regions of cultivation on the quality of the ginger rhizomes. © 2020 Society of Chemical Industry.

Application of electronic nose as a non-invasive technique for odor fingerprinting and detection of bacterial foodborne pathogens: a review.

Food safety issues across the global food supply chain have become paramount in promoting public health safety and commercial success of global food industries. As food regulations and consumer expectations continue to advance around the world, notwithstanding the latest technology, detection tools, regulations and consumer education on food safety and quality, there is still an upsurge of foodborne disease outbreaks across the globe. The development of the Electronic nose as a noninvasive technique suitable for detecting volatile compounds have been applied for food safety and quality analysis. Application of E-nose for pathogen detection has been successful and superior to conventional methods. E-nose offers a method that is noninvasive, fast and requires little or no sample preparation, thus making it ideal for use as an online monitoring tool. This manuscript presents an in-depth review of the application of electronic nose (E-nose) for food safety, with emphasis on classification and detection of foodborne pathogens. We summarise recent data and publications on foodborne pathogen detection (2006-2018) and by E-nose together with their methodologies and pattern recognition tools employed. E-nose instrumentation, sensing technologies and pattern recognition models are also summarised and future trends and challenges, as well as research perspectives, are discussed.

Application of Hyperspectral Imaging as a Nondestructive Technique for Foodborne Pathogen Detection and Characterization.

Microbial food safety is a persistent and exacting global issue due to the multiplicity and complexity of foods and food production systems. Foodborne illnesses caused by foodborne bacterial pathogens frequently occur, thus endangering the safety and health of human beings. Factors such as pretreatments, that is, culturing, enrichment, amplification make the traditional routine identification and enumeration of large numbers of bacteria in a complex microbial consortium complex, expensive, and time-consuming. Therefore, the need for rapid point-of-use detection systems for foodborne bacterial pathogens with high sensitivity and specificity is crucial in food safety control. Hyperspectral imaging (HSI) as a powerful testing technology provides a rapid, nondestructive approach for pathogen detection. This article reviews some fundamental information about HSI, including instrumentation, data acquisition, image processing, and data analysis-the current application of HSI for the detection, classification, and discrimination of various foodborne pathogens. The merits and demerits of HSI for pathogen detection as well as current and future trends are discussed. Therefore, the purpose of this review is to provide a brief overview of HSI, and further lay emphasis on the emerging trend and importance of this technique for foodborne pathogen detection.

Xylopia aethiopica Seeds from Two Countries in West Africa Exhibit Differences in Their Proteomes, Mineral Content and Bioactive Phytochemical Composition.

Aside from its multiple medicinal uses, the fruit of Xylopia aethiopica is widely used in Africa as food. Herein, we characterize the protein profiles, mineral content and bioactive phytochemical composition of the seeds of this plant sourced in Ghana and Nigeria. Using label-free proteomics, a total of 677 proteins were identified, with 260 found in the Ghana-sourced samples while 608 proteins were detected in the samples from Nigeria. However, 114 proteins were common between the samples from the two countries, among which 48 were significantly changed. Bioinformatics and functional analyses revealed that the differential levels of the proteins were mainly linked to pathways involved amino acids metabolism and biosynthesis. The significantly changed proteins related mainly to catalytic activity and carbon metabolism. The samples from Nigeria also exhibited superior qualities in terms of their antioxidant effects, and total phenolic and flavonoid content. Finally, only the content of Na varied to a statistically significant level. This study lends support to its culinary use and hints towards the impact of location of cultivation on the quality of the seeds. There is however need for further mechanistic investigations to unravel the underlying reasons for the observed differences.

Accumulation of heavy metals and human health risk assessment of vegetable consumption from a farm within the Korle lagoon catchment.

The Korle lagoon is known to have high concentration of heavy metals. The use of land for agriculture and water for irrigation within the Korle Lagoon's catchment constitutes a potential health risk. Due to this, the study assessed the concentration of heavy metals in some vegetables (Amaranth, Spinach, Eggplant, Lettuce, Cauliflower, and Onion) and their corresponding soil from a farm within the Korle Lagoon's catchment. The estimated daily intake (EDI), hazard quotient (HQ), and lifetime cancer risk (LCR) was used to assess their health risks. Among the vegetables tested, heavy metals in lettuce exceeded their recommended guideline level. Additionally, the concentrations of Fe (265.94-3599.60 mg/kg) and Zn (76.77-294.70 mg/kg) in all vegetables were above the recommended guideline level. Also, Zn (227.30-534.57 mg/kg) and Pb (101.53-407.58 mg/kg), in soil were above the recommended guideline level for soil. The results also showed not only the severity of heavy metal pollution of soil in the study area, but also risks that were deemed carcinogenic and noncarcinogenic to both adults and children as a result of consumption of vegetables from the study area. The hazard index for adults (0.46-41.156) and children (3.880-384.122), were high for all vegetables tested and are associated with cancer risk due to high Cr and Pb levels. The risk assessment showed that children may suffer more carcinogenic and noncarcinogenic health risk than adults. The study concluded that vegetables grown within the Korle lagoon's catchment is not suitable for consumption due to the associated adverse health effect.

Sonication, osmosonication and vacuum-assisted osmosonication pretreatment of Ghanaian garlic slices: Effect on physicochemical properties and quality characteristics.

This work aimed to assess the impact of sonication (US), osmosonication (US + OD) and vacuum-assisted osmosonication (V + US + OD) pretreatments on the quality of Ghanaian garlic prior to relative humidity convective drying. Hence, slices of fresh garlic subjected to US, US + OD and V + US + OD pretreatments were dried and the following assessed: antioxidant activities, total phenolic content (TPC), total flavonoid content (TFC), polyphenol oxidase (PPO) enzyme inactivation, rehydration ratio (RR), drying kinetics, energy consumption, chromatographic fingerprinting, allicin content and Fourier-transform infrared (FT-IR) spectroscopy. V + US + OD pretreatment gave the best results for antioxidant activities, TPC, TFC, RR and PPO enzyme inactivation. It also recorded the shortest drying time and was more energy efficient. Finally V + US + OD pretreatment maintained the chemical integrity of the finished product and recorded the highest content of allicin. A general trend was however observed for all quality parameters assessed for the various pretreatment methods as: V + US + OD > US + OD > US.

Vacuum pressure combined with osmosonication as an innovative pre-drying technique for Ghanaian ginger: Evidence from the metabolome and quality characteristics of the dried product.

We assessed the impact of selected pretreatment techniques, thus, vacuum-assisted osmotic dehydration (VOD), vacuum-assisted sonication (VSON) and vacuum-assisted osmosonication (VOS) on the metabolomes and quality characteristics of infrared-dried ginger slices. We found marked metabolome differences between the pretreated ginger samples, evidenced by differential amounts of 6-gingerol and 6-shogaol, total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activities. We also found distinct differences in the drying kinetics and sensory characteristics of the pretreated samples. Generally, VOS pretreatment gave the best outcomes. The VOS-pretreated samples contained the highest contents of the marker compounds, TPC, TFC and gave the best antioxidant activity. The VOS-pretreated samples also recorded the shortest drying time and exhibited the best sensory attributes. Overall, the general order observed was, VOS > VSON > VOD > control for all quality parameters examined. VOS pretreatment of ginger before drying therefore holds a great potential for large-scale industrial application.

Effects of Various Nonthermal Pretreatments on the Physicochemical Properties of Dried Ginger (Zingiber officinale Roscoe) Slices from Two Geographical Locations.

This study explored the effect of different nonthermal pretreatments, osmosonication (OS), osmotic dehydration, and ultrasound methods on the physical and chemical properties of China- and Ghana-sourced ginger samples under relative humidity convective drying. The chemical properties of pretreated dried ginger slices were assessed for antioxidant properties (ABTS and DPPH); total phenolic content; total flavonoids content; and 4-, 6-, 8-, and 10-gingerol and 6-shogaol levels. The physical properties compared were weight loss, rehydration ratio (RR), texture, and drying kinetics. Results revealed that OS pretreatment led to a higher preservation of the chemical properties with the Ghana-sourced ginger exhibiting the highest values. The OS-treated samples obtained the highest weight losses and RRs, but the RR was higher in the Chinese ginger. OS pretreatment also gave the lowest textural value with the China-sourced samples exhibiting the lowest firmness. Weibull model best fitted the experimental results (R2 > 0.99). PRACTICAL APPLICATION: Ginger remains among the most notable medicinal spices worldwide. It is used as a raw material for the pharmaceutical, beverage, cosmetics, and the food industries. Long-term storage of ginger is one of paramount importance, hence any pretreatment that reduces its moisture content and lessens its drying time but preserves its quality is ideal. In this study, we report the effect of different nonthermal pretreatments, osmosonication, osmotic dehydration, and ultrasound on the physical and chemical properties of China- and Ghana-sourced ginger samples under relative humidity convective drying. The present findings will offer more information in the selection of the best pretreatment technique for drying ginger.

Effects of ultrasound, osmotic dehydration, and osmosonication pretreatments on bioactive compounds, chemical characterization, enzyme inactivation, color, and antioxidant activity of dried ginger slices.

The effect of ultrasound (US), osmotic dehydration (OD), and osmosonication (OS) pretreatments on total phenolic content (TPC), total flavonoids content, (TFC), phytochemical constituents (gingerol derivatives and diarylheptanoids), polyphenol oxidase (PPO), peroxidase (POD), 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid (ABTS), cupric ion reducing capacity (CUPRAC), 1,1-diphenyl-2-picrylhydrazyl (DPPH), ferric reducing antioxidant power capacity (FRAP), and color of ginger slices dried under relative humidity convective dryer was investigated. OS pretreatment improved the preservation of TPC (13.80-34.79 mg GAE/g d.w), TFC (26.46-62.16 mg CE/g d.w), ABTS (30.37%-86.10%), CUPRAC (36.89-73.97 mg/g), DPPH (50.57%-92.60%), FRAP (26.44-83 mg/g), and phytochemical constituents than US and OD. The OS-treated sample was more effective in inactivating both PPO (12.09%-35.93%) and POD (16.21%-39.58%) enzymes compared to US and OD-treated samples. However, US pretreatment retained the color quality of dried ginger slices than the OS and OD treatments. OS pretreatment (5.43) also increased the total color change (ΔE) of the dried ginger samples compared to US (2.81) and OD (4.60). PRACTICAL APPLICATIONS: Ginger is commonly used in the food, beverage, and pharmaceutical industries owing to their distinctive flavor and various health potentials. However, its high moisture content makes its inappropriate for long-term storage which results in its high perishability. Drying is one of the most common techniques to prolong its shelf life. Hence, any pretreatment for ginger that reduces the moistures content and lessens the drying time by preserving the quality of the crop is of vital importance. Ultrasound, osmotic dehydration, and osmosonication are novel pretreatment techniques that are widely used prior to drying of various agricultural products due to its numerous advantages over conventional methods. Its application in drying of foods could help shorten the drying time, reduce processing costs, improve energy consumption and efficiency, and preserve the physical and nutritional properties of the dried product. The current findings will also offer more information for selecting pretreatment techniques for ginger drying.

Carrier Effects on the Chemical and Physical Properties of Freeze-Dried Encapsulated Mulberry Leaf Extract Powder.

In this study mulberry leaf extract biocompounds were encapsulated with sodium carboxymethyl cellulose (0.55%, 0.70%, and 0.75% w/v) or maltodextrin (8%, 10%, and 12% w/v). The outcome of this work demonstrated that maltodextrin showed the highest encapsulation efficiency towards the phenolic acids and 1-deoxynojirimycinin whereas the flavonols and gamma-aminobutyric acid were best encapsulated by sodium carboxymethyl cellulose. Moreover, the antioxidant properties of the encapsulated powders were found to be associated with their nutraceutical constituents. In addition, the powders produced with sodium carboxymethyl cellulose were typified by suitable hygroscopicity, wettability time, glass transition temperature, and bulk properties than those obtained with maltodextrin which was characterized by desirable porosity, water solubility, moisture content, water activity, color, particle, and flowability properties.