Effect Of Gastrointestinal Digestion Research Articles

Optimization of Extraction Process and Activity of Angiotensin-Converting Enzyme (ACE) Inhibitory Peptide from Walnut Meal.

In order to further realize the resource reuse of walnut meal after oil extraction, walnut meal was used as raw material to prepare polypeptide, and its angiotensin-converting enzyme (ACE) inhibitory activity was investigated. The ACE inhibitory peptides were prepared from walnut meal protein by alkaline solution and acid precipitation. The hydrolysis degree and ACE inhibition rate were used as indexes to optimize the preparation process by single-factor experiment and response surface method. The components with the highest ACE activity were screened by ultrafiltration, and their antioxidant activities were evaluated in vitro. The effect of gastrointestinal digestion on the stability of walnut peptide was analyzed by measuring molecular weight and ACE inhibition rate. The results showed that the optimal extraction conditions were pH 9.10, hydrolysis temperature 54.50 °C, and hydrolysis time 136 min. The ACE inhibition rate of walnut meal hydrolysate (WMH) prepared under these conditions was 63.93% ± 0.43%. Under the above conditions, the fraction less than 3 kDa showed the highest ACE inhibitory activity among the ACE inhibitory peptides separated by ultrafiltration. The IC50 value of scavenging ·OH free radical was 1.156 mg/mL, the IC50 value of scavenging DPPH free radical was 0.25 mg/mL, and the IC50 value of scavenging O2- was 3.026 mg/mL, showing a strong total reducing ability. After simulated gastrointestinal digestion in vitro, the ACE inhibitory rate of walnut peptide decreased significantly, but it still maintained over 90% ACE inhibitory activity. This study provides a reference for the application of low-molecular-weight walnut peptide as a potential antioxidant and ACE inhibitor.

Effect of gastrointestinal digestion on the stability, antioxidant activity, and Caco-2 cellular transport of pigmented grain polyphenols.

Grain polyphenols are known to possess several health properties. However, their digestive stability and intestinal absorption have not been fully elucidated. This study investigated the fate of pigmented grain polyphenols in the digestive system. Purple rice, purple barley, purple wheat, and blue wheat extracts were subjected to simulated gastric and intestinal phase digestion, followed by Caco-2 cellular transport. Phenolic profiling and antioxidant activity were determined using benchtop assays and an ultra-high-performance liquid chromatography-2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid free radical) (UHPLC-ABTS•+ ) system. The results demonstrated a decrease in the total phenolic content of extracts after digestion, with purple rice extract retaining the highest phenolic content (79%) and ABTS•+ antioxidant activity (31%). Antioxidant activity was retained the most during the gastric phase; however, dominant antioxidant compounds were not detected after intestinal digestion. Significant variations in phenolic composition and radical scavenging activity were detected after digestion. Protocatechuic acid, vanillic acid, apigenin, and chrysoeriol were all transported across the intestinal barrier. The findings of this study provide novel insights into the in vitro stability and antioxidant activity of cereal grain polyphenols after simulated digestion.

Effects of gastrointestinal digestion on the cell bioavailability of sodium alginate coated liposomes containing DPP-IV inhibition active collagen peptides

Delivery matrices in foods need to be carefully designed for optimal delivery and to ensure that beneficial compounds are subsequently absorbed in the gut. It has been found that polysaccharide coating improved the cellular uptake of liposomes, but there is a lack of research on the effect of digestion on the cellular uptake of polysaccharide-coated liposomes. Herein, the sodium alginate-coated liposomes were prepared, combination of Caco-2, HT29 and Caco-2/HT29 cell models were used to assess the effect of digestion behavior on the bioavailability. Where, the bioavailability of digested liposomes was 1.60 times higher than that of undigested liposomes. Specifically, digestion firstly improved the ability of liposomes to penetrate the mucus layer by 1.43-fold. Secondly, digestion improved the uptake of liposomes into the intestinal cells by about 1.33-fold. Next, cellular uptake mechanisms were explored using uptake inhibition experiments. Proteomics and metabolic process experiments showed that liposomes pass intact through the small intestinal epithelium into the somatic circulation. This work suggested that digestive behavior enhanced liposome bioavailability in terms of penetration through the cellular mucus layer as well as uptake capacity. These results deepen the understanding of the specific role of digestion on polysaccharide-modified liposomes and favor a better design of delivery systems.

Effect of Gastrointestinal Digestion on the Bioaccessibility of Phenolic Compounds and Antioxidant Activity of Fermented Aloe vera Juices.

Plant-based beverages are enriched by the fermentation process. However, their biocompounds are transformed during gastrointestinal digestion, improving their bioaccessibility, which is of primary importance when considering the associated health benefits. This study aimed to evaluate the effect of in vitro gastrointestinal digestion on phenolic compound bioaccessibility and antioxidant activity of novel Aloe vera juices fermented by probiotic Enterococcus faecium and Lactococcus lactis. Aloe vera juices were digested using the standardized static INFOGEST protocol. During digestion, phenolic compounds and antioxidant activity (DPPH, ABTS, and FRAP) were accessed. The digestion process was seen to significantly increase the total phenolic content of the fermented Aloe vera juices. The fermentation of Aloe vera increased the bioaccessibility of juice biocompounds, particularly for kaempferol, ellagic acid, resveratrol, hesperidin, ferulic acid, and aloin. The phenolics released during digestion were able to reduce the oxidative radicals assessed by ABTS and FRAP tests, increasing the antioxidant action in the intestine, where they are absorbed. The fermentation of Aloe vera by probiotics is an excellent process to increase the bioavailability of beverages, resulting in natural added-value functional products.

Lipid-lowering effect of microencapsulated peptides from brewer's spent grain in high-sucrose diet-fed rats

Brewer's spent grain (BSG) -a byproduct generated from the processing of beer-brewing industry-is currently recognized as an important source of bioactive peptides with potential health benefits. In previous studies we demonstrated that peptides obtained from BSG (BSG-P) can exert in vitro biofunctional activities including hypolipidemic effects. However, there are no studies about the effects of gastrointestinal digestion on BSG lipid-lowering peptides and it is unknown whether the bioactive properties observed in vitro remain in vivo. The aims of this work were to evaluate the microencapsulation as strategy to preserve hypolipidemic BSG-P under a simulated gastrointestinal digestion, and the bioavailability of microencapsulated BSG-P using a rodent model of hyperlipidemia and other metabolic-related disorders induced by the consumption of a high-sucrose diet. In vitro studies showed that microencapsulation improved the BSG-P reduced hypolipidemic activity observed under a simulated gastrointestinal digestion by increasing the inhibition of the fat digestion enzymes, pancreatic lipase and cholesterol esterase. Furthermore, in vivo studies demonstrated that microencapsulated BSG-P were also able to reduce the increased serum lipid levels (triglycerides-TG- cholesterol and free fatty acids), energy intake, visceral adipocytes size and TG content observed in sucrose-rich diet-fed rats. This was accompanied by reduced liver lipids levels and the activities of key enzymes involved in dietary fat absorption. Therefore, our findings show that microencapsulation is a useful strategy to preserve the hypolipidemic activity of BSG-P and support the concept that microencapsulated BSG-P would be an interesting and cheaper natural source to prevent hyperlipidemias and its related-disorders.

Characterization of native lactic acid bacteria from traditionally fermented chhurpi of Sikkim Himalayan region for the production of chhurpi cheese with enhanced antioxidant effect

Lactic acid bacteria (LAB) were isolated and characterized from chhurpi, a traditionally produced cheese product of Sikkim Himalaya. Enterococcus durans was the most dominant LAB making up 34% of the identified LAB, followed by Lactobacillus delbrueckii (25%). Chhurpi was produced using milk curdling LAB strains followed by simulated in vitro gastrointestinal digestion of chhurpi. Evaluation of protein hydrolysis and antioxidant activity was performed. Chhurpi produced using Lactobacillus delbrueckii WS4 had a relatively higher yield (10.4%), protein hydrolysis, and antioxidant activity as compared to other starter strains (P < 0.05). Gastrointestinal digestion of chhurpi increased the antioxidant activity, with the highest activity observed for gastrointestinal digests of chhurpi produced by using Lb. delbrueckii WS4. The EC50 for DPPH radical scavenging activity of chhurpi produced by using Lb. delbrueckii WS4 was observed to decrease significantly (from 239.16 to 48.87 mg sample/ml) after digestion with pepsin and pancreatin (P < 0.05). Protein hydrolysis and antioxidant activity in whey were comparable to that of chhurpi, indicating the potential of using the chhurpi whey to develop nutraceuticals. This is the first report on evaluating the antioxidant activity of chhurpi produced using defined LAB strains and the effect of gastrointestinal digestion on chhurpi functionality.

Effects of in vitro simulated digestion on the antioxidant activity of different Camellia sinensis (L.) Kuntze leaves extracts

The stability of tea phenolic compounds is influenced by pH value and digestive processes. However, the complex mixture of constituents in tea may modulate the stability of these compounds during digestion. In this study, tea infusions obtained from green, black, and Oolong tea leaves were exposed to in vitro simulated gastrointestinal digestion, and the stability of ( +)-catechin, caffeine, (−)-epicatechin, epigallocatechin-3-gallate (EGCG), and gallic acid was compared to that of isolated compounds. Changes in antioxidant activity were also evaluated by means of DPPH assay and in a H2O2-induced in vitro oxidative stress model, using Caco-2 cells. The stability of teas antioxidant constituents was different when using teas extract, compared to the reference compound alone, with the total phenolic content being more stable in extracts containing them in higher amount. EGCG degradation correlated well with changes in the DPPH inhibition assay, confirming its pivotal role in the antioxidant activity of tea. Differently, the antioxidant effect in the in vitro cell-based model was much more related to the initial total phenolic content of the extracts, with green tea being more effective than black tea and Oolong tea. Moreover, the antioxidant activity of teas was strongly affected by gastrointestinal digestion. Taken together, these findings suggest a protective role of teas phytocomplex against gastrointestinal digestion of antioxidant constituents. In conclusion, the effect of gastrointestinal digestion on the antioxidant activity of tea should be taken into account, as this may be different from one extract to another and information on the stability of active constituents cannot be extrapolated from data obtained using single compounds.

Effects of combined application of high‐pressure processing and active coatings on phenolic compounds and microbiological and physicochemical quality of apple cubes

In recent years the use of high-pressure processing (HPP) of fruit products has steadily increased due to its antimicrobial effectiveness and the retention of nutritional and quality attributes compared to conventional thermal technologies. Edible coatings are already being used to enhance the quality of minimally processed fruits. Thus, apple cubes (AC) and alginate-vanillin-coated apple cubes (AVAC) were subjected to HPP (400 MPa/5min/35 °C). The microbiological and physicochemical parameters were evaluated and the bioactive compounds were monitored before and after HPP of apple cubes. Also, an in vitro gastrointestinal digestion (GID) was conducted. HPP left L. monocytogenes counts below the detection limit (2log UFC g-1 ), regardless of the presence of coating. For E. coli, HPP + active coating showed a synergism affording the greatest reduction (>5log) for AVAC-HPP. Firmness was maintained in AVAC-HPP samples, while AC-HPP samples suffered reductions of 35%. Colour attributes were also better retained in AVAC-HPP samples. In general, HPP led to a decrease in phenolic compounds. Regarding the effects of GID, vanillin-based active coating exerted a protective effect on some phenolics. Thus, p-coumaroylquinic acid concentration was maintained for AVAC and AVAC-HPP during GID. Epigallocatechin, the compound with the highest concentration in apple cubes, increased for AVAC (106%) and AVAC-HPP (57%). Also, phloridzin concentration increased for AVAC-HPP (17%). At the end of GID, procyanidin B1 and epigallocatechin were the main phenolic compounds for all samples, AVAC showing the highest concentration. This work demonstrates that the combined application of HPP and active coatings on apple cubes could be used to obtain a safe and good-quality product. © 2021 Society of Chemical Industry.

Effect of in vitro gastrointestinal digestion on phenolic compounds and the antioxidant activity of Aloe vera

Abstract The aim of this work is to study the effect of digestion on the total polyphenol content, flavonoids and the antioxidant activity of Aloe vera. Total polyphenol contents and flavonoid spectrophotometric methods: The evaluation of the antioxidant activity was carried out by three methods, DPPH, ABTS and CUPRAC. To confirm the results obtained we carried out an analysis by ATR-FTIR. The total phenol content found in the Aloe vera extract studied was 1.3638 mg EAG/100 g, while the content of flavonoids found in the Aloe vera extract studied was 0.690 mg EQ/100 g. The values of total polyphenols and flavonoids decreased under the effect of gastrointestinal digestion. The spectra obtained during the ATR-FTIR analysis show that Aloe vera is rich in phenolic compounds and flavonoids. Intense bands corresponding to O–H bonds, C=C bond, C–H, CO, CH3 and CH2 confirm the presence of these bioactive compounds. For both the DPPH and CUPRAC methods, Aloe vera extract reveals a strong antioxidant activity, which gradually decreases during the oral and gastric phase and then increases after the intestinal digestion. For the ABTS method, the antioxidant activity decreases during the oral phase, increases during the gastric phase and then decreases again during the intestinal phase.

Effect of in-vitro digestion on the bio active compounds and biological activities of fruit pomaces.

The effect of gastro intestinal digestion on total phenolic contents (TPC), total flavonoid contents (TFC), radical scavenging activity (RSA) and vitamin C levels of apple (Malus domestica) pomace and a local variety of jujube (Ziziphus mauritiana) pomace was evaluated after drying at 110°C for 3h in a hot air oven. The physicochemical properties and functional properties of apple and jujube pomaces were also assessed. Prior to digestion, apple pomace displayed greater levels of TPC, RSA and vitamin C (17.30 ± 0.59 GAE/g DW, 81.16 ± 3.27%, 0.078 ± 0.01g/L, respectively) in comparison with jujube pomace (16.90 ± 0.66 GAE/g DW, 54.65 ± 2.09%, 0.069 ± 0.01g/L, respectively), whereas, TFC level was found to be higher in jujube pomace (19.22 ± 0.87 QE/g DW). After digestion, both samples showed an increase in TPC (56.17 ± 2.14 and 52.01 ± 2.18 GAE/g DW for apple and jujube pomaces) and TFC levels (48.45 ± 1.87 and 53.82 ± 2.34 QE/g DW for apple and jujube pomaces) and it was perceived almost 3 to 4 times higher than the TPC and TFC of the samples before digestion. But, RSA of the fruit pomaces were found to be affected by the in vitro digestion which was observed as 54.65 ± 2.09 and 81.16 ± 3.27% respectively for apple and jujube pomaces. It may be suggested that the fruit powders may be incorporated in developing new functional foods rich in bio active compounds and thus can be utilized in different food applications.

Molecular action mechanism of anti-inflammatory hydrolysates obtained from brewers' spent grain.

Brewers' spent grain (BSG) is a relevant, protein-rich by-product of the brewing process. Protein hydrolysates from different sources exert immune-regulatory actions activating toll-like receptors (TLRs), nuclear factor kappa B (NFκB), and mitogen-activated protein kinases (MAPKs). Effects of gastrointestinal digestion have been poorly studied. Here, we studied the immune-regulatory effect of BSG hydrolysates, and their in-vitro-digested products, on rat splenocytes, macrophages, and T lymphocytes RESULTS: In primary cultures of rat spleen cells, BSG hydrolysates induced interleukin 10 and tumor necrosis factor production in basal conditions. Under stimulation with lipopolysaccharide or concanavalin A, hydrolysates further induced interleukin 10 production. Tumor necrosis factor and interferon-γ were inhibited in lipopolysaccharide- and concanavalin-A-stimulated cells respectively. In vitro gastrointestinal digestion attenuated the observed effects. Splenic macrophages and T lymphocytes behaved in a similar fashion. In spleen cells from TLR2-/- and TLR4-/- mice, immune-regulatory effects were greatly reduced or abrogated. The study of signal transduction pathways indicated a major involvement of NFκB, and the contribution of MAPKs p38, c-Jun N-terminal kinase, and extracellular signal-regulated kinases 1 and 2. BSG hydrolysates, like those obtained from other food sources, regulate the immune response, involving TLR2 and TLR4 and the activation of NFκB and MAPKs, an effect partly maintained after in vitro gastrointestinal digestion. Our data support the hypothesis of a shared, rather unspecific, mechanism of action of protein hydrolysates. © 2020 Society of Chemical Industry.

In vitro effect of green tea and turmeric extracts on GLP-1 and CCK secretion: the effect of gastrointestinal digestion.

Plant extract activity can be modified by the digestion process. In order to assess the satiety effect of green tea and turmeric extracts, an in vitro gastrointestinal digestion process was performed and the STC-1 cell line was used. The enteroendocrine cell line was incubated (for 30, 60 and 120 minutes) with the digested and non-digested extracts measuring the secretion of cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) by enzyme-linked immunosorbent assay (ELISA). The release of satiety hormones by the STC-1 cells showed similar or higher results for plant extracts compared to the positive controls reported as satiatogenic (proteins and short chain fatty acids). For the non-digested samples, the largest amount of CCK and GLP-1 was found for turmeric, with 379 ± 46 pg ml-1 (60 min) and 347 ± 125 pg ml-1 (120 min) respectively. For the digested samples, the highest level of CCK was found for turmeric at 30 minutes (43.3 ± 11) and for GLP-1 by green tea at 120 minutes (165.7 ± 52). The in vitro gastrointestinal digestion process affects the satiety of plant extracts, increasing for green tea and decreasing for turmeric. Green tea showed the most stable satiating capacity after the in vitro digestion process and this may be useful for using it as a stable food supplement to reduce hunger associated with overweight and obesity.

Effects of simulated gastrointestinal digestion on the physicochemical properties, erythrocyte haemolysis inhibitory ability and chemical antioxidant activity of mulberry leaf protein and its hydrolysates

SummaryProteins and peptides must be degraded and modified in the gastrointestinal (GI) tract prior to absorption; this process changes their physicochemical and biological properties. Mulberry leaf protein (MP) and its hydrolysates (HMP) have favourable antioxidant activities. To investigate, in vitro and separately, the effects of GI digestion and intestinal digestion on the stability of MP and HMP, we monitored the changes in secondary structures, amino acids, molecular weights and antioxidant activities. We found that MP was more hydrolysed by pepsin than by pancreatin, unlike HMP. The final digests of MP and HMP were mainly composed of polypeptides (0.5–6.5 kDa) and oligopeptides (&lt;0.5 kDa), respectively. The GI digestion influenced MP and HMP differently; GI digestion increased the antioxidant efficiency of MP and decreased that of HMP. For the intestinal digests, the antioxidant activities of MP and HMP also differed. The 1,1‐diphenyl‐2‐picrylhydrazyl (DPPH) and 2,2′‐azinobis (3‐ethylbenzothiazoline‐6‐sulphonic acid) diammonium salt (ABTS) radical quenching abilities of MP and HMP at 1 mg mL−1 were comparable to or exceeded that of L‐glutathione (GSH) and 6‐hydroxy‐2,5,7,8‐tetramethychroman‐2‐carboxylic acid (trolox). Meanwhile, the erythrocyte haemolysis rates of MP, HMP and their GI products at 0.05–1.0 mg mL−1 were significantly lower than that of the 2,2′‐azobis (isobutyramidine) dihydrochloride (AAPH) control. Both MP and HMP can be used as natural antioxidants and may promote digestive health.

Stability of Bioactive Compounds and Antioxidant Activity of Thai Cruciferous Vegetables during In Vitro Digestion

Raphanus sativus (L.) var. caudatus Alef (Thai rat-tailed radish), Brassica juncea (L.) Czern. (leaf mustard) and Brassica juncea (L.) Coss. var. sareptana Sinskaja (mustard green) are cruciferous vegetable commonly consumed in Thailand and Asian countries. The vegetables were extracted with different solvents namely methanol, hexane and water prior to total phenolic content (TPC), phenethyl isothiocyanate (PEITC) content and antioxidant activity by ferric reducing antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay were determined. Effects of gastrointestinal digestion on stability of these characteristics were investigated. It was found that the order of extraction efficiency for high bioactive compounds and antioxidant activity was water&gt; methanol&gt; hexane. Among vegetables, mustard green showed the highest TPC, PEITC, FRAP and DPPH values being 19.78±0.01 g GAE, 9.65 ± 1.08 µmol, 8.18±0.01 µM FeSO4 and 7.75±0.31 µM TE per 100g, respectively. Decreases in DPPH (30.6-53.5%), FRAP (49.0-88.0%) and PEITC (27.2-56.7%) values were slightly higher than TPC (27.9-41.6%) after in vitro digestion. It can be said that Thai cruciferous vegetables contain substantial chemical property and this may promote their health protection but the stability through digestive system should be warranted.

Effect of in vitro gastrointestinal digestion on the bioavailability of phenolic components and the antioxidant potentials of some Turkish fruit wines

This study was designed to evaluate the effects of in vitro gastrointestinal simulation method on the antioxidant potentials and phenolic profile of some Turkish fruit wines and to compare the results with a Turkish red wine prepared from native grape varieties (Papazkarası). For this purpose, blueberry, black mulberry and cherry wines were studied since they are widely consumed in Turkey. Papazkarası wine was chosen due to the lack of studies regarding this type of wine. Antioxidant potentials of samples were measured with four different methods: DPPH radical-scavenging activity, H2O2-scavenging activity, cupric reducing capacity and total antioxidant capacity assays. The phenolic profiles of samples were evaluated by the determination of total phenolic content and HPLC-DAD analysis of seven different molecules. The results of this study provided information not only the effect of gastrointestinal digestion on parameters mentioned above, but also the bioaccessibility about the phenolic compounds found in these four different wine samples.

Effect of in vitro digestion on bioactive compounds and antioxidant activity of common bean seed coats

The effects of gastrointestinal digestion on black bean (BB) and small red bean (SRB) seed coats were evaluated in treated and untreated extracts with an in vitro digestion process. The total phenols (TPs), total flavonoids (TFs), condensed tannins (CTs), monomeric anthocyanins (MAs), ABTS radical-scavenging capacity and oxygen radical absorbance capacity (ORAC) were evaluated in both groups. Anthocyanins, which appeared at 10-fold higher levels in BB than SRB (0.83mg and 0.08mg cyanidin 3-glucoside equivalents/g of bean, respectively) were undetectable in either extract after digestion. The results indicate that the in vitro digestion process was responsible for a reduction of the TPs, CTs and MAs in both the BB and SRB seed coats, and of TFs in the BB seed coats. However, the antioxidant activity was maintained for both groups, and even significantly increased in the BB group when measured with an ORAC assay.

Anti-inflammatory properties of fruit juices enriched with pine bark extract in an in vitro model of inflamed human intestinal epithelium: The effect of gastrointestinal digestion

Enrichment of fruit juices with pine bark extract (PBE) could be a strategy to compensate for phenolic losses during the gastrointestinal digestion. A coculture system with Caco-2 cells and RAW 264.7 macrophages was established as an in vitro model of inflamed human intestinal epithelium for evaluating the anti-inflammatory capacity of fruit juices enriched with PBE (0.5gL−1) before and after in vitro digestion. The digestion of both PBE-enriched pineapple and red fruit juice led to significant changes in most of the analysed phenolic compounds. The in vitro inflammatory state showed cell barrier dysfunction and overproduction of IL-8, nitric oxide (NO) and reactive oxygen species (ROS). In the inflamed cells, incubation with nondigested samples reduced (P<0.05) the production of IL-8 and NO compared with digested samples. ROS production increased in the inflamed cells exposed to digested commercial red fruit juice (86.8±1.3%) compared with fresh juice (77.4±0.8%) and increased in the inflamed cells exposed to digested enriched red fruit juice (82.6±1.6%) compared with the fresh enriched juice (55.8±6%). The anti-inflammatory properties of PBE-enriched fruit juices decreased after digestion; further research on the bioavailability of the assayed compounds is needed to properly assess their usefulness for the treatment of gut inflammation.

Effects of gastrointestinal digestion and heating on the allergenicity of the kiwi allergens Act d 1, actinidin, and Act d 2, a thaumatin‐like protein

Kiwifruit is a significant elicitor of allergy both in children and adults. Digestibility of two kiwifruit allergens, actinidin (Act d 1) and thaumatin-like protein (Act d 2), was assessed using an in vitro digestion system that approximates physiological conditions with respect to the passage of food through the stomach into the duodenum. Act d 1 precipitated in simulated gastric fluid at pH 2 and digestion of the aggregated protein proceeded slowly. The residual precipitate redissolved completely in simulated duodenal fluid at pH 6.5 and was partially digested. Forty percent of Act d 2 remained intact during gastric digestion and were cleaved by duodenal proteases into large fragments covalently linked by disulfide bonds. Both digested allergen samples displayed nearly unchanged IgE binding abilities. Circular dichroism spectra were used to analyze heat and acid-induced unfolding. Thermal stability of both allergens was strongly pH dependent. While Act d 1 was irreversibly destabilized in acidic solutions, heat-induced denaturation of Act d 2 at pH 2 was fully reversible. IgE binding to Act d 2 but not Act d 1 was detected in processed food products. The stability of Act d 1 and Act d 2 provides one explanation for the allergenic potency of kiwifruit.