Purification and characterization of broad bean lipoxygenase isoenzymes

The challenge of breeding for reduced off-flavor in faba bean ingredients

The growing interest in plant protein sources, such as pulses, is driven by the necessity for sustainable food production and climate change mitigation strategies. Faba bean (Vicia faba L.) is a promising protein crop for temperate climates, owing to its remarkable yield potential (up to 8 tonnes ha-1 in favourable growing conditions) and high protein content (~29% dry matter basis). Nevertheless, the adoption of faba bean protein in plant-based products that aim to resemble animal-derived counterparts is hindered by its distinctive taste and aroma, regarded as "off-flavors". In this review, we propose to introduce off-flavor as a trait in breeding programs by identifying molecules involved in sensory perception and defining key breeding targets. We discuss the role of lipid oxidation in producing volatile and non-volatile compounds responsible for the beany aroma and bitter taste, respectively. We further investigate the contribution of saponin, tannin, and other polyphenols to bitterness and astringency. To develop faba bean varieties with diminished off-flavors, we suggest targeting genes to reduce lipid oxidation, such as lipoxygenases (lox) and fatty acid desaturases (fad), and genes involved in phenylpropanoid and saponin biosynthesis, such as zero-tannin (zt), chalcone isomerase (chi), chalcone synthase (chs), β-amyrin (bas1). Additionally, we address potential challenges, including the need for high-throughput phenotyping and possible limitations that could arise during the genetic improvement process. The breeding approach can facilitate the use of faba bean protein in plant-based food such as meat and dairy analogues more extensively, fostering a transition toward more sustainable and climate-resilient diets.

Faba Bean Flavor Effects from Processing to Consumer Acceptability

Faba beans as an alternative source of protein have received significant attention from consumers and the food industry. Flavor represents a major driving force that hinders the utilization faba beans in various products due to off-flavor. Off-flavors are produced from degradation of amino acids and unsaturated fatty acids during seed development and post-harvest processing stages (storage, dehulling, thermal treatment, and protein extraction). In this review, we discuss the current state of knowledge on the aroma of faba bean ingredients and various aspects, such as cultivar, processing, and product formulation that influence flavour. Germination, fermentation, and pH modulation were identified as promising methods to improve overall flavor and bitter compounds. The probable pathway in controlling off-flavor evolution during processing has also been discussed to provide efficient strategies to limit their impact and to encourage the use of faba bean ingredients in healthy food design.

Origins of volatile compounds and identification of odour-active compounds in air-classified fractions of faba bean (Vicia faba L. minor)

Faba bean (Vicia faba L. minor) has many interests but is characterised by off-notes (negative odours/aromas) due to volatile compounds that are promoted during seed processing. Little is known about the volatile compounds of faba bean and their contribution to its odour. The purpose of this study was to determine the volatile compound origins of air-classified fractions (flour (F), starch (S) and protein (P)) from 3 faba bean cultivars and identify the odour-active compounds. Firstly, the volatile content of the fractions was extracted by solvent-assisted flavour evaporation (SAFE) and analysed by gas chromatography-mass spectrometry (GC-MS). A total of 147 volatile compounds were detected and categorised into 12 chemical classes. The P fractions had many volatile compounds from free fatty acid (FFA) oxidation and a higher lipoxygenase (LOX) activity. The volatile content suggested that cultivar 1 (C1) was confronted with a biotic stress at field whereas cultivar 2 (C2), richer in molecules from amino acid (AA) degradation, was contaminated by microorganisms in the field. Secondly, 35 odour-active compounds (OACs) were identified by GC-olfactometry (GC-O) and 12 odour-classes were used to describe the faba bean odours. The P fractions had higher detection frequency (DF) than the S and F fractions. P2 had a more complex odour profile due to important FFA and AA degradation. This work provides a better understanding of the impact of cultivar and processing steps on the faba bean volatile content. Selection of pulse-based ingredients with low volatile compounds could improve their flavour and increase their consumption.

Flavor challenges in extruded plant-based meat alternatives: A review

Demand for plant-based meat alternatives has increased in recent years due to concerns about health, ethics, the environment, and animal welfare. Nevertheless, the market share of plant-based meat alternatives must increase significantly if they are to support sustainable food production and consumption. Flavor is an important limiting factor of the acceptability and marketability of plant-based meat alternatives. Undesirable chemosensory perceptions, such as a beany flavor, bitter taste, and astringency, are often associated with plant proteins and products that use them. This study reviewed 276 articles to answer the following five research questions: (1) What are the volatile and nonvolatile compounds responsible for off-flavors? (2) What are the mechanisms by which these flavor compounds are generated? (3) What is the influence of thermal extrusion cooking (the primary structuring technique to transform plant proteins into fibrous products that resemble meat in texture) on the flavor characteristics of plant proteins? (4) What techniques are used in measuring the flavor properties of plant-based proteins and products? (5) What strategies can be used to reduce off-flavors and improve the sensory appeal of plant-based meat alternatives? This article comprehensively discusses, for the first time, the flavor issues of plant-based meat alternatives and the technologies available to improve flavor and, ultimately, acceptability.

Specific Roles of Lipoxygenases in Development and Responses to Stress in Plants

Lipoxygenases (LOXs), naturally occurring enzymes, are widely distributed in plants and animals. LOXs can be non-sulfur iron, non-heme iron, or manganese-containing dioxygenase redox enzymes. LOXs catalyze the oxidation of polyunsaturated fatty acids into fatty acid hydroperoxides. Linolenic acid, a precursor in the jasmonic acid (JA) biosynthesis, is converted to 12-oxo-phytodienoic acid through oxygenation with LOX, allene oxide synthase, and allene oxide cyclase. Moreover, JA participates in seed germination, fruit ripening, senescence, and many other physio-biochemical processes. LOXs also play crucial roles in defense responses against biotic stress, i.e., insects, pests, pathogenic attacks, and abiotic stress, such as wounding, UV-rays, extreme temperature, oxidative stress, and drought.

Volatile Compounds in Pulses: A Review

The worldwide demand for pulse-based products is increasing in the face of climate change, but their acceptability is limited due to the presence of off-flavours. Off-notes contribute to negative perceptions of pulses (beany notes). Volatile compounds belong to a large variety of chemical classes. They are mainly produced from the oxidation of unsaturated free fatty acids and the degradation of amino acids during seed development, storage, and transformation (dehulling, milling, and starch or protein production). This review aims to provide an overview highlighting the identification of these molecules in different pulses, their potential origins, and their impact on perceptions. However, data on odour-active compounds in pulses are sparse, as they are limited to those of two studies on peas and lupins. A better knowledge of the volatile compounds involved in the off-notes and their origins should allow for drawing efficient strategies to limit their impact on overall perception for more acceptable healthy food design.

Preliminary Investigations into the Use of Amylases and Lactic Acid Bacteria to Obtain Fermented Vegetable Products

Legumes are valuable sources of proteins and other functional components. However, the high starch content can be an impediment in developing new vegan food formulations. Enzyme-assisted hydrolysis was used to hydrolyze the starch from chickpea and broad bean vegetable milk to further develop vegetable lactic acid-fermented products. The antioxidant activity of legumes was tested, and it was observed that the overall antioxidant activity (DPPH radical scavenging ability) significantly increased after enzyme-assisted hydrolysis while total phenols content decreased. The obtained vegetable milk was then fermented using exopolysaccharides-producing lactic acid bacteria. A significant decolorization was observed after fermentation in the case of broad bean-based products. Rheological behavior of the fermented products was determined using small amplitude oscillatory measurements and the three-interval thixotropy test. Results showed higher complex viscosity values for broad bean-based products, which displayed a weak gel-like structure. The starter cultures used for vegetable milk samples fermentation influenced the resistance to flow.

Fava bean (Vicia faba L.) for food applications: From seed to ingredient processing and its effect on functional properties, antinutritional factors, flavor, and color

The food industry, along with the consumers, is interested in plant-based diet because of its health benefits and environmental sustainability. Vicia faba L. (V. faba) is a promising source of pulse proteins for the human diet and can yield potential nutritional and functional ingredients, namely, flours, concentrates, and isolates, which are relevant for industrial food applications. Different processes produce and functionalize V. faba ingredients relevant for industrial food applications, along with various alternatives within each unit operation used in their production. Processing modifies functional properties of the ingredients, which can occur by (i) changing in overall nutritional composition after processing steps and/or (ii) modifying the structure and conformation of protein and of other components present in the ingredients. Furthermore, V. faba limitations due to off-flavor, color, and antinutritional factors are influenced by ingredient production and processing that play a significant role in their consumer acceptability in foods. This review attempts to elucidate the influence of different ways of processing on the functional, sensory, and safety aspects of V. faba L. ingredients, highlighting the need for further research to better understand how the food industry could improve their utilization in the market.

Food allergens: Classification, molecular properties, characterization, and detection in food sources

Food allergy is a large and growing public health problem in many areas of the world. The prevalence of food allergy has increased in the last decades in a very significant way in many world regions, particularly in developed countries. In that respect, the research field of food allergy has experienced an extensive growth and very relevant progress has been made in recent years regarding the characterization of food allergens, the study of their immunological properties, and their detection in food sources. Furthermore, food labeling policies have also been improved decidedly in recent years. For that immense progress made, it is about time to review the latest progress in the field of food allergy. In this review, we intend to carry out an extensive and profound overview regarding the latest scientific advances and knowledge in the field of food allergen detection, characterization, and in the study of the effects of food processing on the physico-chemical properties of food allergens. The advances in food labeling policies, and methodologies for the characterization of food allergens are also thoroughly reviewed in the present overview.

Potential of faba bean lipase and lipoxygenase to promote formation of volatile lipid oxidation products in food models

Faba bean can respond to the need for plant-based proteins for human consumption. The aim of this work was to study the role of lipid-modifying enzymes in faba bean in causing off-flavour compounds during processing. The faba bean exhibited high lipase and lipoxygenase (LOX) activities, with pH optima being 8.0 and 6.0, respectively. Faba bean LOX preferred free fatty acids (FFAs) over triacylglycerols as substrates, and together with other LOX pathway enzymes, it formed specific volatile products, as measured using headspace solid-phase microextraction-gas chromatography. During the preparation of the food models (i.e. the extracts and emulsions), enzymatic lipid oxidation occurred. The inclusion in the emulsions of rapeseed oil, especially of rapeseed oil FFAs, remarkably increased the amounts of volatile products. The largest quantities of products were formed in food models at pH 6.4, which is close to the pH optimum of LOX. Further studies on lipase in food models are needed.

HPLC Analysis and Biochemical Characterization of LOX from Eschscholtzia californica Cham

BACKGROUND

Plant lipoxygenases (LOXs, EC 1.13.11.12) are involved in lipid degradation, regulation of growth and development, senescence, and defence reactions. LOX represents the starting enzyme of the octadecanoid pathway. The aim of the work was to purify LOX from California poppy (Eschscholtzia californica Cham.), to determine its biochemical properties and to identify and quantify the products of LOX reaction with unsaturated fatty acids.

METHODS

LOX from California poppy seedlings was purified by hydrophobic chromatography (Phenyl-Sepharose CL-4B) and by ion-exchange chromatography (Q-Sepharose). The isolated LOX was incubated with linoleic acid used as a substrate. The HPLC experiments were performed with the Agilent Technologies 1050 series HPLC system. For the preparative separation of a mixture of hydroxy fatty acids from the sample matrix, the RP-HPLC method was used (column 120-5 Nucleosil C18). Then, the NP-HPLC analysis (separation, identification, and determination) of hydroxy fatty acid isomers was carried out on a Zorbax Rx-SIL column.

RESULTS

The purified LOX indicates the presence of a nontraditional plant enzyme with dual positional specificity (a ratio of 9- and 13-hydroperoxide products 1:1), a relative molecular mass of 85 kDa, a pH optimum of 6.5, an increasing activity stimulation by CaCl₂ till 2 mM, and a high substrate reactivity to linoleic acid with kinetic values of KM 2.6 mM and Vmax 3.14 μM/min/mg.

CONCLUSIONS

For the first time, the LOX from California poppy seedlings was partially purified and the biochemical properties of the enzyme were analyzed. A dual positional specificity of the LOX found from California poppy seedlings is in agreement with the results obtained for LOXs isolated from other Papaveraceaes. A 1:1 ratio of 9-/13-HODE is attractive for the simultaneous investigation of both biotic stress responses (indicated by the 9-HODE marker) and the biosynthesis of jasmonic acid and jasmonates (indicated by the 13-HODE marker).

Purification and characterization of lipoxygenase from mung bean (Vigna radiata L.) germinating seedlings

This study reports purification and characterization of lipoxygenase protein from mung bean germinating seedlings. Lipoxygenases (LOXs) are key enzymes in seed germination. The purified mung bean LOX has resolved into two peaks by chromatofocusing, one has highest LOX activity with an isoelectric point of 5.84 and the other has lowest LOX activity with an isoelectric point of 5.52. The purified LOX has molecular mass of approximately 97 kDa and showed high activity with linoleic acid than linolenic acid and arachidonic acid. The optimal activity of LOX was observed at pH 6.5 and temperature 35 °C. Far-UV circular dichroism (CD) studies revealed that the purified mung bean LOX possess secondary structural elements with significant α-helix and β-strands. Further, the secondary structure of mung bean LOX was stable up to 60 °C at pH 6.5. Biophysical and chemical properties of the mung bean LOX are similar to the other legume LOXs and may be considered as type-1 LOX.

Lipoxygenase activity in different species of sweet lupin (Lupinus L.) seeds and flakes

Lipoxygenase (LOX)-catalysed degradation of polyunsaturated fatty acids is supposed to be a major cause of undesirable off-flavour development in legumes. In the present study, a photometric LOX assay including adequate sample workup was adapted to lupin seeds, kernels and flakes, respectively. Optimum reaction conditions were at pH 7.5 using a phosphate buffer concentration of 150 mmol l(-1) without the addition of sodium chloride. The LOX activities of different lupin species and varieties were compared. Significant variations among the species and varieties ranging from 50 to 1004 units mg(-1) protein were determined, being significantly lower than soybean LOX activity. Hulling and flaking of the seeds resulted in a 15% increase of LOX activity. In contrast to soy and other legumes, LOX from lupin only converted free fatty acids, whereas trilinolein and β-carotene were not oxidised. Consequently, according to the established classification, lupin LOX activity may be assigned to the LOX type-1, which, to the best of our knowledge, was demonstrated for the first time.

Crystal structure and functional insights of hemopexin fold protein from grass pea

A regulatory protein from grass pea (Lathyrus sativus), LS-24, a close homolog of albumin 2 from garden pea (Pisum sativum) that is associated with polyamine biosynthesis, was characterized and the structure of a hemopexin-type fold among plant proteins illustrated. Crystal structure of LS-24 determined at 2.2 A resolution by multiple isomorphous replacement phasing showed four-bladed beta-propeller structure having a pseudo 4-fold molecular symmetry along a metal ion-binding central channel. The structure represents typical mammalian hemopexin fold with discernible features correlated with the possible functional variations. The protein was found to exist in the dimeric state. While LS-24 dimer binds to spermine in the crystal structure as well as in solution, binding of heme in solution resulted in the dissociation of the dimer into monomers with concomitant release of bound spermine. Interactions of heme and spermine with LS-24 bear physiological implications. While binding of spermine to LS-24 can be linked with polyamine biosynthesis that of heme correlates with oxidative stress. Mutually exclusive binding of heme and spermine in different oligomeric states suggest a role for LS-24 in sensing oxidative stress through a ligand-regulated monomer-dimer transition switch.

Purification and characterization of soluble Cichorium intybusVar. silvestre lipoxygenase

A water-soluble lipoxygenase enzyme (EC 1.13.11.12; LOX) occurring in the red cultivar produced in the geographical area of Chioggia (Italy) of Cichorium intybus var. silvestre was isolated and characterized. The molecular mass of the enzyme was estimated to be 74,000 Da by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel filtration chromatography. The isoelectric point was pH 6.85. The optimum values of pH, ionic strength, and temperature, shown by isoresponse surface calculated by a randomized multilevel factorial design, were 7.58, 30 mM, and 38.5 degrees C, respectively. The enzyme showed high specificity toward linoleic acid, and the study of the variation of linoleic acid concentration between 30 and 300 microM, in the presence of Tween 20 at a concentration lower than the critical micelle concentration (0.01 v/v), resulted in a typical Michaelis-Mentem curve with KM and Vmax values of 1.49 x 10(-4) M and 2.049 microM min(-1) mg(-1), respectively. The biochemical properties, the kinetic parameters found, and the carotene-bleaching activity shown in aerobic conditions seem to indicate that the isolated enzyme is a lipoxygenase type III according to the indications given for soybean isoenzymes.

The novel pathway for ketodiene oxylipin biosynthesis in Jerusalem artichoke (Helianthus tuberosus) tubers

The new route of the plant lipoxygenase pathway, directed specifically towards the ketodiene formation, was detected during in vitro experiments with Jerusalem artichoke (Helianthus tuberosus) tubers. Through this pathway (9Z,11E,13S)-13-hydroperoxy-9,11-octadecadienoic acid (13-HPOD) is reduced to corresponding 13-hydroxy acid (13-HOD), which is in turn dehydrogenated into ketodiene (9Z,11E,13S)-13-oxo-9,11-octadecadienoic acid (13-KOD). Dehydrogenation of 13-HOD into 13-KOD was not dependent on the presence of either NAD or NADP, but was strongly dependent on the presence of oxygen. Under anoxic conditions, 13-HOD dehydrogenation was blocked, but addition of 2,6-dichlorophenolindophenol restored it. Sulfite addition fully suppressed the aerobic dehydrogenation of 13-HOD. Hydrogen peroxide is a by-product formed by the enzyme along with 13-KOD. These data suggest that the ketodiene biosynthesis in H. tuberosus tubers is catalyzed by flavin dehydrogenase. (9S,10E,12Z)-9-Hydroxy-10,12-octadecadienoic acid (9-HOD) is dehydrogenated by this enzyme as effectively as 13-HOD, while alpha-ketol, (9Z)-12-oxo-13-hydroxy-9-octadecenoic acid, and ricinoleic acid did not act as substrates for dehydrogenase. The enzyme was soluble and possessed a pH optimum at pH 7.0-9.0. The only 13-HOD dehydrogenase known so far was detected in rat colon. However, unlike the H. tuberosus enzyme, the rat dehydrogenase is NAD-dependent.

Functional properties, lipoxygenase activity, and health aspects of Lupinus albus protein isolates

To utilize lupin seeds for food and pharmaceutical applications, lupin seeds were pretreated to remove oil using hexane or carbon dioxide. Two types of lupin protein isolate were prepared. Both types of protein isolate showed good foaming activity, comparable to egg white. Protein isolate extracted under acid conditions showed higher foaming activity than protein isolate extracted at neutral pH. The lipoxygenase activity was much reduced in both of the protein isolates. The protein isolate extracted at neutral pH showed a stronger angiotensin converting enzyme inhibition than the protein isolate extracted under acidic pH. In contrast, the protein isolate extracted under acid conditions had a greater sodium cholate binding capacity, comparable to that of cholestyramine. Lupin samples showed less DPPH radical scavenging activity than deoiled soybean. The deoiling method did not affect the functional properties, lipoxygenase activity, angiotensin converting enzyme inhibition, sodium cholate binding, and radical scavenging activity.

Purification and characterization of lipoxygenase from Pleurotus ostreatus

Lipoxygenase was purified homogeneously from cups of Pleurotus ostreatus by Sephacryl S-400 HR gel filtration, Dyematrex Green A affinity, and DEAE-Toyopearl 650M ion-exchange chromatographies. The molecular weight of the enzyme was estimated to be 67,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 66,000 by gel filtration; the isoelectric point was pH 5.1. The optimum pH and temperature of the enzymatic activity were 8.0 and 25 degrees C, respectively. The enzyme contained non-heme iron, and a thiol group seemed to be involved in its activity. The K(m), V(max), and k(cat) values of the enzyme for linoleic acid were 0.13 mM, 23.4 micromol.min(-1).mg(-1), and 25.7 s(-1), respectively. The enzyme showed high specificity toward linoleic acid. When linoleic acid was incubated with the enzyme, 13-hydroperoxy-9Z,11E-octadecadienoic acid was found to be the main oxidative product.