A review of drying methods for improving the quality of dried herbs.

A large number of herb-drying studies have been conducted in recent decades and several herb-drying techniques have been introduced. However, the quality of commercial dried herbs is still lower than that of fresh herbs. In this paper, studies regarding the effect of drying techniques and pre-drying treatments on the aroma and color of dried herbs are reviewed with the aim of providing an overview of different technological strategies developed for improving the quality of aromatic herbs for their industrial drying.

Effects of Storage Conditions on Degradation of Chlorophyll and Emulsifying Capacity of Thylakoid Powders Produced by Different Drying Methods.

Thylakoid membranes isolated from spinach have previously been shown to inhibit lipase/co-lipase and prolong satiety in vivo. There is a need to develop thylakoid products that not only have the desired characteristics and functionality after processing, but also are stable and provide equivalent effect on appetite over the promised shelf life. The aim of the present study was therefore to evaluate how the thylakoid powders' characteristics and functionality were affected by moisture during storage. Thylakoids produced by drum-drying, spray-drying, and freeze-drying were incubated in controlled atmosphere with different relative humidity (10 RH%, 32 RH%, 48 RH% and 61 RH%) for 8 months. The water content in all powders was increased during storage. The water absorption was moisture-dependent, and the powders were considered hygroscopic. Relative humidity showed a definite influence on the rate of chlorophyll degradation and loss of green color in thylakoid powders after storage which correlated with impaired emulsifying capacity. Spray-dried powder had the overall highest chlorophyll content and emulsifying capacity at all RH-levels investigated. Spray drying was therefore considered the most suitable drying method yielding a powder with best-maintained functionality after storage. The results can be applied towards quality control of high-quality functional foods with appetite suppressing abilities.

Early and advanced stages of Maillard reaction in infant formulas: Analysis of available lysine and carboxymethyl-lysine.

Although the literature on the Maillard reaction in infant formulas is extensive, most studies have focused on model systems, and in only a few cases on real food systems. Therefore, the objective of the present study was to determine the status of the Maillard reaction, both the early and advanced phases, in a variety of commercial infant formulas available on the Swedish market. Ten powder and liquid milk-based infant formulas from three manufacturers were selected to determine available lysine and CML contents, the two established indicators of the reaction. The products were also characterized with respect to protein content, carbohydrates composition, water content and water activity. In order to be able to compare the impact of different processing steps applied on powder and liquid formulas, the solid formulas contained similar ingredients as their corresponding liquid ones. Our findings showed that powder and liquid formulas contained similar available lysine concentrations regardless of the manufacturer, showing 27.14-36.57% decrease in the available lysine, compared to the reference skim milk powder in this study. The CML concentrations were in a broad range of 68.77-507.99 mg / kg protein. In the case of one manufacturer, liquid infant formulas had significantly higher CML content, compared to the powder products (p < 0.05). The results from this study are a step taken towards better understanding of the extent of the Maillard reaction in real complex systems of infant formulas.

Chemical methods and techniques to monitor early Maillard reaction in milk products; A review.

Maillard reaction is an extensively studied, yet unresolved chemical reaction that occurs as a result of application of the heat and during the storage of foods. The formation of advanced glycation end products (AGEs) has been the focus of several investigations recently. These molecules which are formed at the advanced stage of the Maillard reaction, are suspected to be involved in autoimmune diseases in humans. Therefore, understanding to which extent this reaction occurs in foods, is of vital significance. Because of their composition, milk products are ideal media for this reaction, especially when application of heat and prolonged storage are considered. Thus, in this work several chemical approaches to monitor this reaction in an early stage are reviewed. This is mostly done regarding available lysine blockage which takes place in the very beginning of the reaction. The most popular methods and their applications to various products are reviewed. The methods including their modifications are described in detail and their findings are discussed. The present paper provides an insight into the history of the most frequently-used methods and provides an overview on the indicators of the Maillard reaction in the early stage with its focus on milk products and especially milk powders.

Daily Intake of Milk Powder and Risk of Celiac Disease in Early Childhood: A Nested Case-Control Study.

Milk powder and gluten are common components in Swedish infants' diets. Whereas large intakes of gluten early in life increases the risk of celiac disease in genetically at-risk Swedish children, no study has yet evaluated if intake of milk powder by 2 years of age is associated with celiac disease. A 1-to-3 nested case-control study, comprised of 207 celiac disease children and 621 controls matched for sex, birth year, and HLA genotype, was performed on a birth cohort of HLA-DR3-DQ2 and/or DR4-DQ8-positive children. Subjects were screened annually for celiac disease using tissue transglutaminase autoantibodies (tTGA). Three-day food records estimated the mean intake of milk powder at ages 6 months, 9 months, 12 months, 18 months, and 24 months. Conditional logistic regression calculated odds ratios (OR) at last intake prior to seroconversion of tTGA positivity, and for each time-point respectively and adjusted for having a first-degree relative with celiac disease and gluten intake. Intake of milk powder prior to seroconversion of tTGA positivity was not associated with celiac disease (OR = 1.00; 95% CI = 0.99, 1.03; p = 0.763). In conclusion, intake of milk powder in early childhood is not associated with celiac disease in genetically susceptible children.

Characteristics and functionality of appetite-reducing thylakoid powders produced by three different drying processes.

BACKGROUND: Thylakoids, a chloroplast membrane extracted from green leaves, are a promising functional ingredient with appetite-reducing properties via their lipase-inhibiting effect. Thylakoids in powder form have been evaluated in animal and human models, but no comprehensive study has been conducted on powder characteristics. The aim was to investigate the effects of different isolation methods and drying techniques (drum-drying, spray-drying, freeze-drying) on thylakoids' physicochemical and functional properties. RESULTS: Freeze-drying yielded thylakoid powders with the highest lipase-inhibiting capacity. We hypothesize that the specific macromolecular structures involved in lipase inhibition were degraded to different degrees by exposure to heat during spray-drying and drum-drying. We identified lightness (Hunter's L-value), greenness (Hunter's a-value), chlorophyll content and emulsifying capacity to be correlated to lipase-inhibiting capacity. Thus, to optimize the thylakoids functional properties, the internal membrane structure indicated by retained green colour should be preserved. This opens possibilities to use chlorophyll content as a marker for thylakoid functionality in screening processes during process optimization. CONCLUSION: Thylakoids are heat sensitive, and a mild drying technique should be used in industrial production. Strong links between physicochemical parameters and lipase inhibition capacity were found that can be used to predict functionality. The approach from this study can be applied towards production of standardized high-quality functional food ingredients. © 2017 Society of Chemical Industry.

Application of a dye-binding method for the determination of available lysine in skim milk powders.

A dye-binding method using Acid Orange 12 was investigated regarding its suitability for the quantification of available lysine, as a means of monitoring the Maillard reaction in skim milk powders. The method was evaluated by analyzing a wide range of milk powders produced by three different drying methods and stored under various conditions. A pilot-scale freeze-dryer, spray-dryer and drum-dryer were used to produce skim milk powders and the samples were stored at two temperatures (20 °C and 30 °C) and two relative humidities (33% and 52%) under strictly controlled conditions. Moreover to validate the method, two protein isolates; bovine serum albumin and casein were investigated for their available lysine content. The results demonstrate the suitability of this method for measuring the available lysine in skim milk powders with good precision and high reproducibility. The relative standard deviations obtained from the 125 freeze-dried powders were 1.8%, and those from the 100 drum-dried samples were all 1.9%. The highest variation was found for the spray-dried powders, which showed relative standard deviations between 0.9% and 6.7%.

The effect of heat treatment of thylakoids on their ability to inhibit in vitro lipase/co-lipase activity.

Thylakoids has been shown to prolong lipolysis by the inhibition of lipase/co-lipase, which makes thylakoids suitable as a functional food ingredient with satiating properties. The components of thylakoids that provide its function as a lipolysis modulator are primarily photosystems I and II, which are structurally stabilised by chlorophyll. However, chlorophyll is known to be heat sensitive yet the enzymatic inhibiting capacity after heat treatment has not been previously studied. It was hypothesised that the retained function of thylakoids after heat treatment could be correlated to the degree of degradation. Heat treatment at either 60 °C, 75 °C or 90 °C for time interval ranging from 15 s to 120 min induced a color shift from bright green to olive brown which was attributed to degradation. The ability of heat-treated thylakoids to inhibit lipolysis in vitro was also reduced. A correlation between chlorophyll a degradation and the enzymatic inhibiting capacity could be established which opens possibilities to use a spectrophotometric method to quantify the ability of thylakoids to inhibit lipase/co-lipase in a more rapid and cost effective way to complement the pH-stat method used today. With the degradation pattern investigated, it is then possible to design a thermal treatment process to ensure a microbiological safe appetite-reducing product and at the same time minimize the loss of functionality.

Proximate analysis of five wild fruits of Mozambique.

Mozambique is rich in wild fruit trees, most of which produce fleshy fruits commonly consumed in rural communities, especially during dry seasons. However, information on their content of macronutrients is scarce. Five wild fruit species (Adansonia digitata, Landolphia kirkii, Sclerocarya birrea, Salacia kraussii, and Vangueria infausta) from different districts in Mozambique were selected for the study. The contents of dry matter, fat, protein, ash, sugars, pH, and titratable acidity were determined in the fruit pulps. Also kernels of A. digitata and S. birrea were included in the study. The protein content in the pulp was below 5 g/100 g of dry matter, but a daily intake of 100 g fresh wild fruits would provide up to 11% of the recommended daily intake for children from 4 to 8 years old. The sugar content varied between 2.3% and 14.4% fresh weight. The pH was below 3, except for Salacia kraussii, for which it was slightly below 7. Kernels of A. digitata contained, on average, 39.2% protein and 38.0% fat, and S. birrea kernels 32.6% protein and 60.7% fat. The collection of nutritional information may serve as a basis for increased consumption and utilization.

Dietary fiber, organic acids and minerals in selected wild edible fruits of Mozambique.

The harvesting, utilization and marketing of indigenous fruits and nuts have been central to the livelihoods of the majority of rural communities in African countries. In this study we report on the content of dietary fiber, minerals and selected organic acids in the pulps and kernels of the wild fruits most commonly consumed in southern Mozambique. The content of soluble fiber in the pulps ranged from 4.3 to 65.6 g/100 g and insoluble fiber from 2.6 to 45.8 g/100 g. In the kernels the content of soluble fiber ranged from 8.4 to 42.6 g/100 g and insoluble fiber from 14.7 to 20.9 g/100 g. Citric acid was found in all fruits up to 25.7 g/kg. The kernels of Adansonia digitata and Sclerocarya birrea were shown to be rich in calcium, iron, magnesium and zinc. The data may be useful in selecting wild fruit species appropriate for incorporation into diets.

Effect of steam cooking on the residual enzymatic activity of potatoes cv. Agria.

BACKGROUND: The aim of this work was to study the influence of steam cooking on pectin methylesterase (PME) and endogenous α- and ß-amylase activities in different tissues (cortex and pith) of raw and heat-treated potatoes cv. Agria. Three different cooking temperatures were chosen (55, 70 and 85 °C). For each cooking trial, time-temperature profiles were recorded and the degree of cooking was expressed in terms of cooking factor. RESULTS: Steam cooking contributed to significantly activate PME at 55 °C and to reduce its activity at the final processing temperature (85 °C), with the highest amount in the cortex (0.3745 ± 0.0007 µmol galacturonic acid (GA) g(-1) fresh weight (FW) min(-1) ) compared with the pith (0.2617 ± 0.0012 µmol GA g(-1) FW min(-1) ). The presence of heat-labile and heat-stable isoforms of PME in the considered potato tissues was also assumed. Heat treatment by steam resulted in a significant decrease in endogenous α- and ß-amylase activities in both tissues compared with the raw potato, though without complete deactivation. Starch-degrading enzymes were also found to be differently distributed in the raw tuber. CONCLUSION: Steam cooking affected in different ways the assessed residual enzymatic activity in the considered tissues of potatoes cv. Agria. Further research is needed to confirm the results obtained.

Impact of harvest year on amino acids and sugars in potatoes and effect on acrylamide formation during frying.

Acrylamide is formed via the Maillard reaction between reducing sugars and asparagine in a number of carbohydrate-rich foods during heat treatment. High acrylamide levels have been found in potato products processed at high temperatures. To examine the impact of harvest year, information on weather conditions during growth, that is, temperature, precipitation, and light, was collected, together with analytical data on the concentrations of free amino acids and sugars in five potato clones and acrylamide contents in potato chips (commonly known as crisps in Europe). The study was conducted for 3 years (2004-2006). The contents of acrylamide precursors differed between the clones and the three harvest years; the levels of glucose were up to 4.2 times higher in 2006 than in 2004 and 2005, and the levels of fructose were 5.6 times higher, whereas the levels of asparagine varied to different extents. The high levels of sugars in 2006 were probably due to the extreme weather conditions during the growing season, and this was also reflected in acrylamide content that was approximately twice as high as in preceding years. The results indicate that acrylamide formation is dependent not only on the content and relative amounts of sugars and amino acids but also on other factors, for example, the food matrix, which may influence the availability of the reactants to participate in the Maillard reaction.

Acrylamide in home-prepared roasted potatoes.

Potato is one of the world's most widely grown tuber crop, in which starch is the predominant form of carbohydrates. Potatoes can be prepared in many ways: boiled, fried or roasted. Frying and roasting potatoes at high temperatures result in an appetizing crust, but at the same time acrylamide can form. In this study, the concentrations of the acrylamide precursors, asparagine and sugars, were determined in five different Swedish-grown potato varieties, together with the acrylamide content after typical home-cooking procedures; oven-roasting of potato wedges and pan-frying of cubes of boiled potatoes. Pan-frying of boiled potato cubes resulted in higher levels of acrylamide (530-1100 microg/kg) than in the wedges (140-250 microg/kg). Blanching combined with a shorter roasting time was shown to be an efficient way of reducing the acrylamide content in roasted potato wedges, especially in the experiments performed after long-term storage, where the acrylamide content was reduced from 110-260 to 50-140 microg/kg. No correlation was found between precursor content and acrylamide content, and this finding emphasizes the need for further studies on factors affecting acrylamide formation, for example, the availability of precursors at the surface during cooking.

A study on the use of empirical models to predict the formation of acrylamide in potato crisps.

The formation of acrylamide in potato crisps was fitted by empirical mathematical models. Potato slices were fried under the same experimental conditions for different times. Besides the content of precursors in the raw potato slices, acrylamide and water content in the potato crisps were quantified after predetermined times (2-6 min). The temperature developments in the surrounding oil and outer cell layer of the potato slices were monitored, giving more insight in the frying process and making future comparisons between studies possible. The pattern found for the formation of acrylamide, which was similar to earlier studies, was fitted to three empirical models. Statistical methods were used to compare the performance of the models, with the "Logistic-Exponential" and "Empirical" model performing equally well. The obtained model parameters were in the range of earlier reported studies, although this comparison is not unequivocal as the experimental conditions differed between studies. The precision of parameter estimates was problematic; this should be improved by better experimental design. Nevertheless, the approach of this study will make it possible to truly compare acrylamide formation patterns and model parameters in the future, with the ability to develop a tool to predict acrylamide formation in potato crisps.

Plant stress physiology: opportunities and challenges for the food industry.

We review and analyze the possible advantages and disadvantages of plant-stress-related metabolic and structural changes on applications in the fruit and vegetable processing industry. Knowledge of the cellular and tissue transformations that result from environmental conditions or industrial manipulation is a powerful means for food engineers to gain a better understanding of biological systems in order to avoid potential side effects. Our aim is to provide an overview of the understanding and implementation of physiological and biochemical principles in the industrial processing of fruits and vegetables.

Factors affecting quality and postharvest properties of vegetables: integration of water relations and metabolism.

Growing of vegetables in the field, harvesting, handling in the packing house and storage are events in the lifetime of vegetables that are analysed from the point of view of the complex series of physiological transitions taking place in each of these events. Water is the major factor limiting plant metabolism and plants have developed fascinating mechanisms to cope with this limiting factor. Therefore, water relations (water, pressure and osmotic potential) are used as criteria for discussing plant stress physiology aspects such as osmotic, elastic adjustment and cold acclimation, as well as mechanical stress when the vegetable is harvested and during handling in the packing house. Consequences for the storage potential and quality of the vegetable are discussed. After harvesting, the postharvest cell has the ability to complete a complex series of physiological transitions that will influence vegetable quality andfurther processing operations. Metabolic changes in the cytosol, cell membrane and cell wall are described.

Antioxidants, low molecular weight carbohydrates, and total antioxidant capacity in strawberries (Fragaria x ananassa): effects of cultivar, ripening, and storage.

Four cultivars of strawberries (Senga Sengana, BFr77111, Elsanta, and Honeoye) were studied for their content of antioxidants, total antioxidant capacity, and low molecular weight carbohydrates in relation to harvest year, ripening stage, and cold storage. For ascorbic acid, chlorogenic acid, ellagic acid, and total antioxidative capacity, measured in both water-soluble and water-insoluble extracts, there was a 2-5-fold variation among cultivars. Unripe berries contained lower concentrations of chlorogenic acid and p-coumaric acid and also quercetin and kaempferol compared with riper berries. During cold storage for up to 3 days, relatively few changes in the concentration of the different antioxidants occurred. The concentrations of several investigated parameters were interrelated, for example, for ascorbic acid and water-soluble antioxidant capacity and for ellagic acid and water-insoluble antioxidant capacity. The dominating sugars in strawberries were fructose and glucose, but considerable amounts of sucrose were also present, and their contents varied among cultivars, giving a predicted glycemic index of approximately 81. Verbascose, raffinose, and stachyose were found in only minor amounts. The study shows that the concentration of a number of bioactive compounds in strawberries varied according to cultivar, ripening stage, and storage. This information should make it possible to select strawberries with an optimal content of bioactive compounds.

Influence of temperature, modified atmosphere packaging, and heat treatment on aroma compounds in broccoli.

The aroma compounds in broccoli stored in different modified atmospheres were studied. The packaging materials used were oriented polypropylene (OPP), poly(vinyl chloride) (PVC), and low-density polyethylene (LDPE) containing an ethylene-absorbing sachet. All samples were stored for either 1 week at a constant temperature of 10 degrees C or for 3 days at 4 degrees C, followed by 4 days at 10 degrees C. The atmospheres that developed inside the packaging materials differed significantly. The broccoli samples were analyzed raw and after cooking, with regard to volatile compounds, using gas-phase (headspace) extraction followed by gas chromatography-mass spectrometry (GC-MS) and GC-olfactometry. Dimethyl sulfide (DMS), dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), hexanal, 3-cis-hexen-1-ol, nonanal, ethanol, and a group of thiocyanates were selected for a detailed study because these compounds cause off-odor and can be used as indicators of stress. Significant differences were found in the aroma profiles of the broccoli samples relative to the packaging materials used for storage. Storage in OPP (14% O(2), 10.5% CO(2)) resulted in most of the off-odors, while storage in LDPE (6% O(2), 7% CO(2)) and PVC (17.9% O(2), 4% CO(2)) was found to maintain the concentration of DMS, DMDS, and DMTS during storage. Heat treatment of the broccoli increased the content of aroma compounds as well as the number of compounds containing sulfur.

Addition of various carbohydrates to beef burgers affects the formation of heterocyclic amines during frying.

The influence of the addition of carbohydrates with different physicochemical properties on weight loss and formation of heterocyclic amines (HAs) during the frying of beef burgers was examined. Furthermore, the capability of carbohydrates to bind HAs was tested. Beef burgers containing 1.5% NaCl and 0.3% tripolyphosphate (reference), with the addition of 1.5% carbohydrate, were fried for 5 min at 200 degrees C in a double-sided pan fryer. The beef burgers were analyzed for HAs with solid phase extraction and liquid chromatography/mass spectrometry. 2-Amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3,4,8-trimethylimidazo[4,5-f]quinoxaline (4,8-DiMeIQx), 2-amino-1-methyl-6-phenyl-imidazo[4,5-b]pyridine (PhIP), and 9H-pyrido[3,4-b]indole (Norharman) were detected in all of the beef burgers. The addition of carbohydrates affected both the weight loss and the formation of HAs during cooking. The formation of HAs could be correlated to depend on both the weight loss and the type of the added carbohydrate. Of the 11 different carbohydrates tested, raw potato starch was most capable of inhibiting the formation of HAs, while potato fiber gave the lowest weight loss and a comparably low amount of PhIP. Wheat bran and potato fiber were found to reversibly bind HAs. It is concluded that adding small amounts of certain carbohydrates may be a simple and effective way of reducing the amount of HAs and can easily be applied in households and commercial preparations of beef burgers.

Mechanisms and prevention of plant tissue collapse during dehydration: a critical review.

The appearance and functional properties are primordial in the quality assessment of semifinished fruit and vegetable products. These properties are often associated with shrunken, shriveled, darkened materials of poor rehydration ability after been subjected to air-drying--the most used drying method in the food industry. Fruits and vegetables are cellular tissues containing gas-filled pores that tend to collapse when subjected to dehydration. Collapse is an overall term that has different meanings and scale-settings in the literature depending on whether the author is a plant physiologist, a food technologist, a chemical engineer, or a material scientist. Some clarifications are given in this particular but wide field. The purpose of this work was to make a state-of-the-art contribution to the structural and textural effects of different types of dehydration on edible plant products and give a basis for preventing this phenomenon. The plant tissue is described, and the primordial role of the cell wall in keeping the structural integrity is emphasized. Water and its functionality at macro and micro levels of the cellular tissue are reviewed as well as its transport during dehydration. The effects of both dehydration and rehydration are described in detail, and the term "textural collapse" is proposed as an alternative to structural collapse.