Potential of different mechanical and thermal treatments to control off-flavour generation in broccoli puree

Identification of volatile and flavor metabolites in three varieties of broccoli sprouts

Broccoli sprouts are promising functional food sources and their taste and flavor play a pivotal role in the acceptance of consumers. In this study, the flavor profiles of three varieties of broccoli sprouts, namely Bi Lv, You Xiu, and Lv Hua, were comprehensively characterized using HS-SPME-GC/MS analysis. A total of 364 volatile and flavor components across 15 chemical classes were successfully identified. The results revealed a majority of volatile metabolites exhibiting upregulation during the germination process, leading to an enhancement in taste intensity after germination, particularly for umami and sweet tastes, which was associated with an increase in associated amino acids and sugar content. Although the total glucosinolate content in broccoli sprouts has decreased compared to seeds, it remains the primary contributor to the bitterness of broccoli sprouts. The present study elaborated on the flavor contribution of broccoli sprouts, supporting the cultivation and consumption of them as a nutritious food.

Ectoine maintains the flavor and nutritional quality of broccoli during postharvest storage

The bacterial derived osmolyte ectoine has been shown to stabilize cell structure and function, a property that may help to extend the shelf life of broccoli. The impact of ectoine on broccoli stored for 4 d at 20 °C and 90% relative humidity was investigated. Results indicated that 0.20% ectoine treatment maintained the quality of broccoli, by reducing rate of respiration and ethylene generation, while increasing the levels of total phenolics, flavonoids, TSS, soluble protein, and vitamin C, relative to control. Headspace-gas chromatography-mass spectrometry, transcriptomic and metabolomic analyses revealed that ectoine stabilized aroma components in broccoli by maintaining level of volatile compounds and altered the expression of genes and metabolites associated with sulfur metabolism, as well as fatty acid and amino acid biosynthesis pathways. These findings provide a greater insight into how ectoine preserves the flavor and nutritional quality of broccoli, thus, extending its shelf life.

How do pretreatment and frozen storage impact the volatile profiles of Brussels sprouts and leek?

The volatile profiles of Brussels sprouts and leek, as affected by pretreatment combined with frozen storage were analyzed in the present work. The data revealed that, notwithstanding the effect upon pretreatment seemed to be major compared to the effect upon frozen storage, the latter was existent. Pretreatment yielded volatile compounds that could be associated with (bio)chemical reaction pathways in both vegetables. For frozen storage at -20 °C, the effect for leek appeared to be the largest for the blanched and raw samples, possibly due to a substantial amount of substrates present when frozen storage was initiated in this sample compared to the other samples. Those substrates were apparently more prone to be affected upon frozen storage. For Brussels sprouts, this observation was less outspoken. Remarkably, the abundance of markers in pretreated Brussels sprouts seemed to show a decreasing linear trend towards the end of the frozen storage period at -20 °C. As industrial relevant conditions were considered and compared, the insights gained in this study might be relevant to implement on industrial level.

The volatile profile of pasteurized leek (Allium ampeloprasum var. porrum) and Brussels sprouts (Brassica oleracea var. gemmifera) (products), as a witness to (bio)chemical reactivity, influenced by pretreatment and successive refrigerated storage

Processing can affect (bio)chemical conversions in vegetables and can act on their volatile properties accordingly. In this study, the integrated effect of pretreatment and pasteurization on the volatile profile of leek and Brussels sprouts and the change of this profile upon refrigerated storage were investigated. Pretreatments were specifically selected to steer biochemical reactivities to different extents. Volatile profiles were analyzed by headspace-solid phase microextraction-gas chromatography-mass spectrometry. For both vegetables, it was observed that different pretreatments prior to a pasteurization step led to diverse volatile profiles. The differences in volatile profiles observed in the different samples were presumably attributed to the different degrees of enzymatic conversions, further conversions of enzymatically formed products and thermally induced reactivities. Interestingly, the observed initial relative differences between volatile profiles of differently pretreated pasteurized samples were still observed after a refrigerated storage of 4 weeks at 4 °C. In conclusion, refrigerated storage only limitedly affected the resulting volatile profile.

The Volatile Profile of Brussels Sprouts (Brassica oleracea Var. gemmifera) as Affected by Pulsed Electric Fields in Comparison to Other Pretreatments, Selected to Steer (Bio)Chemical Reactions

Pulsed electric fields (PEF) at low field strength is considered a non-thermal technique allowing membrane permeabilization in plant-based tissue, hence possibly impacting biochemical conversions and the concomitant volatile profile. Detailed studies on the impact of PEF at low field strength on biochemical conversions in plant-based matrices are scarce but urgently needed to provide the necessary scientific basis allowing to open a potential promising field of applications. As a first objective, the effect of PEF and other treatments that aim to steer biochemical conversions on the volatile profile of Brussels sprouts was compared in this study. As a second objective, the effect of varying PEF conditions on the volatile profile of Brussels sprouts was elucidated. Volatile fingerprinting was used to deduce whether and which (bio)chemical reactions had occurred. Surprisingly, PEF at 1.01 kV/cm and 2.7 kJ/kg prior to heating was assumed not to have caused significant membrane permeabilization since similar volatiles were observed in the case of only heating, as opposed to mixing. A PEF treatment with an electrical field strength of 3.00 kV/cm led to a significantly higher formation of certain enzymatic reaction products, being more pronounced when combined with an energy input of 27.7 kJ/kg, implying that these PEF conditions could induce substantial membrane permeabilization. The results of this study can be utilized to steer enzymatic conversions towards an intended volatile profile of Brussels sprouts by applying PEF.

An Overview on Effects of Processing on the Nutritional Content and Bioactive Compounds in Seaweeds

The effect of the different processing technologies and the extraction techniques on the bioactive compounds and nutritional value of seaweeds is reviewed in this study. This work presents and discusses the main seaweeds treatments such as drying, heating, and culinary treatments, and how they affect their nutritional value, the bioactive compounds, and antioxidant capacity. Some examples of traditional and green extraction technologies for extracting seaweeds bioactive components are also presented. The last trends and research on the development of seaweed-based food products is also covered in this review. The use of environmentally friendly extraction procedures, as well as the development of new healthy seaweed-based foods, is expected to grow in the near future.

The Impact of Drying and Rehydration on the Structural Properties and Quality Attributes of Pre-Cooked Dried Beans

Fresh common beans can be made ‘instant’ to produce fast-cooking beans by first soaking and cooking the beans before drying to create a shelf-stable product that can be rehydrated at the time of use. This study investigated the interplay between the drying process (air, vacuum and freeze drying), the microstructure and functional attributes of rehydrated pre-cooked beans. The microscopic study revealed that the three different drying techniques resulted in distinctly different microstructures, with the freeze drying process resulting in highly porous materials, while the air- and vacuum-dried samples underwent shrinkage. Additionally, the rehydration behavior (modeled using empirical and diffusion models) demonstrates that the high rehydration rate of freeze-dried beans is due to capillarity, while rehydration, in the case of air- and vacuum-dried beans, is primarily diffusion-controlled. Irrespective of the drying technique, the high rehydration capacity supports little to no structural collapse or damage to the cell walls. The color and texture of the rehydrated beans did not differ greatly from those of freshly cooked beans. The total peak area of the volatiles of rehydrated beans was significantly reduced by the drying process, but volatiles characteristic of the cooked bean aroma were retained. This new understanding is beneficial in tailoring the functional properties of pre-cooked dry convenient beans requiring short preparation times.

Effect of different combined mechanical and thermal treatments on the quality characteristics of garlic paste

The aim of this study was to investigate the effects of the sequence of different thermal and mechanical treatments on the physicochemical parameters and microstructure of garlic paste, in order to improve the quality of the product. The total organosulfur compounds (OSCs) decreased steadily in blended-heated garlic, whereas OSCs decreased sharply after 2 min at 75 °C or 5 min at 85 and 95 °C in heated-blended garlic. After blanching for 5 min, allicin could maintain over 4.0 mg/g only at 75 °C; and OSCs of heated-blended garlic paste were found to drop by 29.56%, 90.63% and 94.79% at 75, 85 and 95 °C, respectively. In blended-heated garlic, the color values of L* (lightness) and a* (redness) decreased (P < 0.05), while the b* (yellowness) and C* (chroma) increased (P < 0.05), obtaining green discoloration garlic paste. The total color differences of blended-heated samples were greater than 12.08, which were 2-6 folds higher compared with heated-blended garlic. Total phenolic content and antioxidant activity decreased (P < 0.05) in all thermal treatments, thermal treatment of heated-blended garlic less than 5 min maintained over 30% of antiradical activity. The sequence of unit operations determined the pattern of garlic microstructure disruption, resulting in various enzymic and non-enzymic reactions. Our results indicated that use of heat treatment prior to blend processing is an effective and feasible method to inhibit garlic discoloration and retain high content of bioactive OSCs. It is recommended that garlic paste be prepared using heated-blended processing, with thermal processing limited to 75 °C for less than 5 min.

Effect of blanching and freezing on the physical properties, bioactive compounds, and microstructure of garlic (Allium sativum L.)

The aim of this work was to evaluate the impact of blanching on the physical properties of frozen garlic cloves and to explore the relationship between quality changes and microstructure. A short-term blanching treatment (100 °C  for 45 s, 90 °C  for 45 s, and 80 °C  for 60 s) before freezing did not affect the total organosulfur compound content. In a preliminary research, blanching conditions were determined to be 100 °C  for 45 to 80 s. Under these conditions, peroxidase was inactivated, but organosulfur compounds were retained. Mechanical and color tests showed a damaging effect of blanching and freezing on frozen garlic blanched for 60 and 80 s at 100 °C . Compared to frozen fresh garlic, frozen garlic treated by blanching for 45 s at 100 °C  retained 2871.49 ± 200.24 µg/g of allicin, although 81.83% of peroxidase was inactivated; browning and hardness improved by 49.97 and 48.01%, respectively. According to scanning electron microscopy, significant damage to the microstructure was observed in both frozen fresh garlic and frozen garlic after 60 s and 80 s of blanching at 100 °C . Moreover, ¹ H low-field nuclear magnetic resonance (LF-NMR) indicated that blanching for 60 s and 80 s induced an increase in free water in garlic tissues, resulting in further damage after freezing. As peroxidase was efficiently inactivated, the microstructure and organosulfur compounds were better preserved, and blanching treatment at 100 °C  for 45 s before freezing is a potential method for obtaining frozen garlic with high sensory and nutritional qualities. PRACTICAL APPLICATION: Freezing helps to overcome challenges associated with growing seasons and the deterioration of garlic during storage. After frozen garlic is thawed, it is prone to some undesirable changes, such as enzymatic browning and softening. Minimal blanching (45 s at 100 °C ) pretreatment can help to maintain the bioactive compounds of garlic and prevent texture and color deterioration caused by freezing directly.

Comprehensive investigation on volatile and non-volatile metabolites in broccoli juices fermented by animal- and plant-derived Pediococcus pentosaceus

A metabolomics approach was employed to investigate differences and correlations among key odorants and non-volatile metabolites in broccoli juices fermented by plant- and animal-derived Pediococcus pentosaceus. Forty volatile metabolites were identified by headspace solid-phase microextraction/gas chromatography-mass spectrometry. According to orthogonal projections to latent structures-differential analysis, 24 and 21 differential volatiles were detected after fermentation by plant- and animal-derived P. pentosaceus, respectively. The concentrations of 10 odorants (OAV ≥ 1) detected by gas chromatography-olfactometry changed significantly after fermentation by P. pentosaceus. Using ultrahigh-pressure liquid chromatography/quadrupole time-of-flight mass spectrometry, 49.47% of the non-volatile metabolites were classified as lipids and lipid-like molecules. The relative expressions of five non-volatile metabolites that exhibited significant correlations with odorants using Spearman correlation analysis changed significantly after fermentation. Fermentation with animal- and plant-derived P. pentosaceus can therefore change key odorants and non-volatile metabolites in broccoli juice that contribute to the characteristic organoleptic properties of products.

Investigation of the effects of mechanical treatments on cellular structure integrity and vitamin C extractability of broccoli (Brassica oleracea L. var. italica) by LF-NMR

Extraction of nutrients from plants is an important unit operation in the food and biological industries. The target nutrient is usually spatially distributed throughout the plant tissue. The intact cell wall and adhering membranes are the main resistances to molecular diffusion. Therefore, disintegration of the intact structure, which in turn increases the permeability of adhering membranes, can significantly improve the nutrient extraction yield and efficiency. In this study, different physical treatments (homogenization, high pressure homogenization, and ball mill grinding) were applied to investigate their effects on the tissue microstructure and the release of vitamin C. The changes in the microstructure were reflected by LF-NMR based on T2 distribution, particle size distribution, and microscopy images. The extraction yield of vitamin C obtained by high-pressure homogenization was increased by 75.69% for floret and 28.84% for stalk, respectively, as compared to that obtained by mechanical homogenization. The degradation of vitamin C was significant due to prolonged operation of the ball mill grinding method although the integrity of the tissues was similar to that of the high-pressure homogenization-treated tissues. This study confirms that the degree of tissue disintegration has a positive correlation with the release of the nutrient (vitamin C) within a limited operating time. LF-NMR has been proven to be an effective method to study the impact of different physical treatments on the cellular structure integrity of plant-originated food materials.