Dietary isoleucine improved flesh quality, muscle antioxidant capacity, and muscle growth associated with AKT/TOR/S6K1 and AKT/FOXO3a signaling in hybrid bagrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂)

Glyphosate combined with TBBPA exposure decreased quality and flavor of common carp (Cyprinus carpio) involved inhibiting muscle growth and collagen synthesis

Glyphosate (N-[phosphonomethyl] glycine, GLY) is the active ingredient of the most widely used commercialized herbicide, and its use increases the potential for co-occurrence with flame retardants such as Tetrabromobisphenol A (TBBPA), posing a threat to aquatic systems and food safety. Therefore, it is important to prioritize evaluating these two compounds' combined toxicity. However, only a few studies have analyzed the effects of pollutant mixing on fish from the perspectives of molecular and nutritional components. In this study, the impact of TBBPA and GLY on muscle development and flesh quality was investigated by exposing common carp to water-borne TBBPA and/or GLY for 30 days. The results showed that TBBPA and GLY exposure decreased the anti-oxidant capacity and content of most free amino acids in common carp muscle. Textural analysis suggested that the meat flesh's hardness, cohesiveness, and chewiness were decreased under TBBPA and GLY exposure. In addition, the decreased cross-sectional area of muscle fibers and collagen deposition were observed in the carp muscle exposed to TBBPA and/or GLY. Further analysis of related genes indicated the co-exposure of TBBPA and GLY significantly upregulated the levels of FoxO1 and MuRF-1, and decreased the levels of MyoD1, Collagen I, α-SMA, and TGF-β. Collectively, our results illustrated that exposure to TBBPA and GLY could inhibit muscle growth and decrease nutritional value in common carp.

Cadmium Pollution Deteriorates the Muscle Quality of Labeo rohita by Altering Its Nutrients and Intestinal Microbiota Diversity

The detrimental effects of cadmium (Cd), a hazardous heavy metal, on fish have triggered global concerns. While the ecotoxicity of Cd on fish has been investigated, the impact of Cd on muscle quality and its correlation with the gut microbiota in fish remains scarce. To comprehensively uncover Cd effects based on preliminary muscle Cd deposition, relevant studies, and ecological Cd pollution data, we exposed Labeo rohita to Cd under concentrations of 0.00 (control), 0.05, and 0.40 mg/L for 30 days and assessed fish health, muscle quality, and intestinal bacterial diversity. We observed significant Cd bioaccumulation in the fish muscle and intestine at 0.40 mg/L treatment, adversely impacting fish health with lower growth indices, higher mortality, behavioral aberrations, and clinical anomalies. More interestingly, Cd exposure decreased muscle quality by reducing nutrient levels, including fat, protein, iron, zinc, mono and polyunsaturated fatty acids, and increasing free amino acids and saturated fatty acids. Elevated oxidative stress markers, including total superoxide dismutase (T-SOD), catalase (CAT), and hydrogen peroxide (H2O2), were detected in the muscles, indicating degraded quality as a result of damage to cellular structures including proteins, lipids, and DNA. Simultaneously, we found Cd exposure altered fish intestinal microbial diversity, impairing muscle nutrient assimilation, thereby influencing muscle quality. Functional predictions suggested a decrease in pathways related to fermentation and chemoheterotrophy in the exposed groups. Overall, this study highlights how Cd toxicity jeopardizes fish health and deteriorates muscle quality which needs to be addressed for human benefit.

Oxidative toxicity mediated oophoritis alters ovarian growth in Channa punctatus under prolonged exposure to herbicide, paraquat dichloride

Herbicide paraquat dichloride, a potent redox agent found its way to natural water bodies and influences their health; however, its impact on the reproductive health of fish is potentially less studied and requires clear investigation. This study was conducted to elucidate its effect on the gonadal health of female fish, Channa punctatus over 60 days. The 96-h LC50 of test herbicide was calculated as 0.24 mL/L for the fish under examination, subsequently, three sub-lethal concentrations were taken in addition to control for the study. The experimental methodology included assessment of oxidative stress markers, hormone levels, expression of interrelated genes, and histological analysis to ascertain the damage to the ovary. At each exposure period, a significant (p < 0.05) rise in endogenous reactive oxygen species in blood cells and activities of oxidative markers in the ovary tissue were observed in treated groups. The gonadosomatic index of the ovary and hormone concentration in plasma decreased at the highest treatment concentration. A significant (p < 0.05) change in the expression of target genes for ovary growth, inflammation, and apoptosis was observed in the treated fish. Histopathological and ultrastructural investigations of the ovary tissue revealed the occurrence of oophoritis and reduced growth of the ovary in herbicide-treated fish. The findings conclude that, herbicide paraquat dichloride causes inflammation in the ovary, in addition to its growth reduction that ultimately, poses a threat to the fish population.

Dietary fishmeal replacement by Clostridium autoethanogenum protein meal influences the nutritional and sensory quality of turbot (Scophthalmus maximus) via the TOR/AAR/AMPK pathways

Clostridium autoethanogenum protein (CAP) is a promising protein source for aquaculture; however, how CAP influences fish quality is worth extensive research. We randomly allocated 630 turbot with initial body weights of about 180 g into 6 groups, with fishmeal-based control diet or diet with CAP replacing 15% (CAP15), 30% (CAP30), 45% (CAP45), 60% (CAP60), or 75% (CAP75) of fishmeal protein. After a 70-d feeding trial, the fillet yield (P = 0.015) and content of protein (P = 0.017), collagen (P < 0.001), hydroxyproline (P < 0.001), C20:5n-3 (P = 0.007), and ∑n-3/∑n-6 polyunsaturated fatty acids ratio (P < 0.001) in turbot muscle was found to decrease linearly with increasing CAP. However, turbot fed CAP15 diet maintained these parameters (P > 0.05). By contrast, the muscle hardness increased linearly with increasing CAP (P = 0.004), accompanied by linear reduction of muscle fiber area (P = 0.003) and expression of myogenesis-related genes, including cathepsin D (ctsd P < 0.001) and muscle ring finger protein 1 (murf 1, P < 0.001). Phosphorylation of protein kinase B (Akt, P < 0.001), target of rapamycin (TOR, P = 0.001), eukaryotic initiation factor 4E-binding protein 1 (4E-BP1, P < 0.001), and ribosomal protein S6 (S6, P < 0.001) decreased linearly; however, phosphorylation of AMP-activated protein kinase (AMPK, P < 0.001), eukaryotic initiation factor 2α (eIF2α, P < 0.001), and the abundance of activating transcription factor 4 (ATF4, P < 0.001) increased with increasing CAP, suggesting that the TOR signaling pathway was inhibited, and the amino acid response (AAR) and AMPK pathways were activated. Additionally, expression of genes related to protein degradation, including myogenic factor 5 (myf 5, P < 0.001), myogenic differentiation (myod, P < 0.001), paired box 7 (pax 7, P < 0.001), and ctsd (P < 0.001), decreased linearly with increasing CAP. In conclusion, CAP could be used to replace up to 15% of fishmeal without negatively impacting turbot quality. However, higher levels of CAP decreased fillet yield, muscle protein content, and muscle fiber diameter while increasing muscle hardness, which could be attributed to the inhibition of the TOR pathway and activation of the AAR and AMPK pathways.

Effects of low protein feed on hepato-intestinal health and muscle quality of grass carp (Ctenopharyngodon idellus)

In this study, grass carp (33.28 ± 0.05 g) were fed three diets for 8 weeks: control (crude protein [CP] 30%, crude lipid [CL] 6%), low protein (LP; CP16%, CL6%), and low protein with high-fat (LPHF; CP16%, CL10%). The final body weight decreased in the LP and LPHF groups compared to the Control (P < 0.05). Liver triglycerides, total cholesterol, and nonesterified fatty acids were higher in the LP group than the Control, whereas these indexes in the LPHF group were higher than those in the LP group (P < 0.05). The LP group had intestinal barrier damage, while the LPHF group had a slight recovery. TNF-α, IL-8, and IL-1β content were lower in the LP group than in the Control (P < 0.05), and even higher in the LPHF group (P < 0.05). The expressions of endoplasmic reticulum stress-related genes Activating transcription factor 6 (ATF-6) and Glucose-regulated protein (GRP78) were higher in the LPHF group against the LP group (P < 0.05). The IL-1β and TNF-α content negatively correlated with intestinal Actinomycetes and Mycobacterium abundance (P < 0.05). The muscle fiber diameter was smaller in both the LP and LPHF groups than the control (P < 0.05), with the LP group showing metabolites related to protein digestion and absorption, and LPHF group exhibiting metabolites related to taste transmission. The results demonstrate reducing dietary protein affects growth, causing liver lipid accumulation, reduced enteritis response, and increased muscle tightness, while increasing fat content accelerates fat accumulation and inflammation.

Exploring the dietary strategies of phenylalanine: Improving muscle nutraceutical quality as well as muscle glycogen and protein deposition in adult grass carp (Ctenopharyngodon idella)

Muscle is the main edible part of bony fish. The purpose of this study was to investigate the influences of phenylalanine (Phe) on muscle quality, amino acid composition, fatty acid composition, glucose metabolism, and protein deposition in adult grass carp. The diets at 2.30, 4.63, 7.51, 10.97, 13.53, and 17.07 g/kg Phe levels were fed for 9 weeks. The results manifested that Phe (10.97-13.53 g/kg) increased the pH of the fillets and decreased muscle cooking loss and lactic acid content; Phe (7.51-17.07 g/kg) improved the composition of the fillets in terms of flavor (free) amino acids, bound amino acids (especially EAA), and fatty acids (especially EPA and DHA); Phe (7.51-13.53 g/kg) increased muscle glycogen content (possibly related to the AMPK signaling pathway) and muscle protein deposition (possibly related to IGF-1/4EBP1/TOR and AKT/FOXOs signaling pathways). In conclusion, a diet with appropriate Phe levels could improve fillet quality.

An insight into role of amino acids as antioxidants via NRF2 activation

Oxidative stress can affect the protein, lipids, and DNA of the cells and thus, play a crucial role in several pathophysiological conditions. It has already been established that oxidative stress has a close association with inflammation via nuclear factor erythroid 2-related factor 2 (NRF2) signaling pathway. Amino acids are notably the building block of proteins and constitute the major class of nitrogen-containing natural products of medicinal importance. They exhibit a broad spectrum of biological activities, including the ability to activate NRF2, a transcription factor that regulates endogenous antioxidant responses. Moreover, amino acids may act as synergistic antioxidants as part of our dietary supplementations. This has aroused research interest in the NRF2-inducing activity of amino acids. Interestingly, amino acids' activation of NRF2-Kelch-like ECH-associated protein 1 (KEAP1) signaling pathway exerts therapeutic effects in several diseases. Therefore, the present review will discuss the relationship between different amino acids and activation of NRF2-KEAP1 signaling pathway pinning their anti-inflammatory and antioxidant properties. We also discussed amino acids formulations and their applications as therapeutics. This will broaden the prospect of the therapeutic applications of amino acids in a myriad of inflammation and oxidative stress-related diseases. This will provide an insight for designing and developing new chemical entities as NRF2 activators.

Effects of Five Lipid Sources on Growth, Hematological Parameters, Immunity and Muscle Quality in Juvenile Largemouth Bass (Micropterus salmoides)

This study investigated the effects of fish oil (FO), soybean oil (SO), rapeseed oil (RO), peanut oil (PO) and lard oil (LO) on growth, immunity and muscle quality in juvenile largemouth bass. After 8 weeks, the results showed that FO and RO could increase weight gain and serum alkaline phosphatase and apelin values compared with LO (p < 0.05). Except lower crude lipid contents, higher amounts of n-3 polyunsaturated fatty acids (15.83% and 14.64%) were present in the dorsal muscle of the FO and RO groups. Meanwhile, FO and RO could heighten mRNA levels of immune defense molecules (lysozyme, hepcidin, and transforming growth factor β1) compared with PO (p < 0.05). While SO could increase potential inflammatory risk via rising counts of white blood cells, platelets, neutrophils and monocytes, and mRNA levels of interleukins (IL-1β, IL-8, IL-12 and IL-15), FO and RO could improve hardness, chewiness and springiness through increasing amounts of hydroxyproline, collagen and lysyl oxidase, and mRNA levels of collagen 1α2 and prolyl hydroxylase in the fish dorsal muscle. Moreover, FO and RO could improve firmness through increasing glycogen and glycogen synthase 1 levels when compared with LO (p < 0.05). Therefore, these results could provide dietary lipid source references during the feeding process of adult largemouth bass.

Dietary isoleucine supplementation enhances growth performance, modulates the expression of genes related to amino acid transporters and protein metabolism, and gut microbiota in yellow-feathered chickens

This study investigated the effects of dietary isoleucine (Ile) on growth performance, intestinal expression of amino acid transporters, protein metabolism-related genes and intestinal microbiota in starter phase Chinese yellow-feathered chickens. Female Xinguang yellow-feathered chickens (n = 1,080, aged 1 d) were randomly distributed to 6 treatments, each with 6 replicates of 30 birds. Chickens were fed diets with 6 levels of total Ile (6.8, 7.6, 8.4, 9.2, 10.0, and 10.8 g/kg) for 30 d. The average daily gain and feed conversion ratio were improved with dietary Ile levels (P < 0.05). Plasma uric acid content and glutamic-oxalacetic transaminase activity were linearly and quadratically decreased with increasing dietary Ile inclusion (P < 0.05). Dietary Ile level had a linear (P < 0.05) or quadratic (P < 0.05) effect on the jejunal expression of ribosomal protein S6 kinase B1 and eukaryotic translation initiation factor 4E binding protein 1. The relative expression of jejunal 20S proteasome subunit C2 and ileal muscle ring finger-containing protein 1 decreased linearly (P < 0.05) and quadratically (P < 0.05) with increasing dietary Ile levels. Dietary Ile level had a linear (P = 0.069) or quadratic (P < 0.05) effect on the gene expression of solute carrier family 15 member 1 in jejunum and solute carrier family 7 member 1 in ileum. In addition, bacterial 16S rDNA full-length sequencing showed that dietary Ile increased the cecal abundances of the Firmicutes phylum, and Blautia, Lactobacillus, and unclassified_Lachnospiraceae genera, while decreased that of Proteobacteria, Alistipes, and Shigella. Dietary Ile levels affected growth performance and modulated gut microbiota in yellow-feathered chickens. The appropriate level of dietary Ile can upregulate the expression of intestinal protein synthesis-related protein kinase genes and concomitantly inhibit the expression of proteolysis-related cathepsin genes.

Dietary threonine improves muscle nutritional value and muscle hardness associated with collagen synthesis in grass carp (Ctenopharyngodon idella)

To further explain the improvement effect of threonine (Thr) on the fillet quality of fish, a 9-week feeding experiment was conducted. After feeding graded levels of Thr (2.38, 5.38, 8.38, 11.38, 14.38 and 17.38 g/kg), the compositions of fillet hydrolyzed amino acid and fatty acid, and the muscle hardness associated with collagen biosynthesis were mainly analyzed in grass carp (Ctenopharyngodon idella). The results showed that Thr increased the pH value, changed the amino acids and fatty acid composition of fillets, especially essential amino acid (EAA), C22:6n3 (DHA) and C20:5n3 (EPA). Furthermore, this study revealed for the first time that the improvement of muscle hardness by Thr was associated with collagen biosynthesis, and the TGF-β1/Smads, LARP6a and Hsp47 regulate transcriptional processes, translation initiation and post-translational modifications in collagen biosynthesis, respectively. This study offered a basis for exploring the contribution of Thr in improving muscle quality in sub-adult grass carp.

Research Note: The influence of different isoleucine: lysine ratios on the growth performance of broiler chickens fed low-protein diets

Two trials were carried out to assess the effects of different ratios of standardized ileal digestible isoleucine:lysine (SID Ile:Lys) on the growth performance of broiler chickens fed low-protein diets. A total of 1,320 male chickens were distributed in each trial into 6 treatments, with 10 replicates with 22 birds each. A control diet was formulated that satisfied the nutritional requirements of the broilers, and a low-protein diet was formulated with reduced protein content, meeting broiler nutritional requirements, except for the SID Ile levels. Five SID Ile:Lys ratios (56%, 61%, 66%, 71%, and 76%) were obtained by adding l-isoleucine to the low-protein diet. The body weight (BW), body weight gain (BWG), average daily feed intake (ADFI), and feed conversion ratio (FCR) were evaluated from day 1 to day 21 in trial 1, and from day 22 to day 44 in trial 2. ANOVA was performed on the data, and the treatments were compared to the control group using Dunnett's test (P ≤ 0.05). Regression analyses were performed for modeling the variables assessed and the ratios of SID Ile:Lys. There was no significant difference between the treatments on ADFI of birds (P > 0.05). The BW, BWG, and FCR showed a quadratic effect as the SID Ile:Lys ratio increased in low-protein diets in trials 1 and 2 (P ≤ 0.05). In conclusion, the recommended ratio of SID Ile:Lys in low-protein diets for growth performance is around 66% for broiler chickens from 1 to 21 d old and is around 65% for broiler chickens from 22 to 44 d old.

Dietary protein levels changed the hardness of muscle by acting on muscle fiber growth and the metabolism of collagen in sub-adult grass carp (Ctenopharyngodon idella)

Background

Nutrient regulation has been proven to be an effective way to improve the flesh quality in fish. As a necessary nutrient for fish growth, protein accounts for the highest proportion in the fish diet and is expensive. Although our team found that the effect of protein on the muscle hardness of grass carp was probably related to an increased collagen content, the mechanism for this effect has not been deeply explored. Moreover, few studies have explored the protein requirements of sub-adult grass crap (Ctenopharyngodon idella). Therefore, the effects of different dietary protein levels on the growth performance, nutritional value, muscle hardness, muscle fiber growth, collagen metabolism and related molecule expression in grass carp were investigated.

Methods

A total of 450 healthy grass carp (721.16 ± 1.98 g) were selected and assigned randomly to six experimental groups with three replicates each (n = 25/replicate), and were fed six diets with 15.91%, 19.39%, 22.10%, 25.59%, 28.53% and 31.42% protein for 60 d.

Results

Appropriate levels of dietary protein increased the feed intake, percentage weight gain, specific growth rate, body composition, unsaturated fatty acid content in muscle, partial free amino acid content in muscle, and muscle hardness of grass carp. These protein levels also increased the muscle fiber density, the frequency of new muscle fibers, the contents of collagen and IGF-1, and the enzyme activities of prolyl 4-hydroxylases and lysyloxidase, and decreased the activity of matrix metalloproteinase-2. At the molecular level, the optimal dietary protein increased collagen type I α1 (Colα1), Colα2, PI3K, Akt, S6K1, La ribonucleoprotein domain family member 6a (LARP6a), TGF-β1, Smad2, Smad4, Smad3, tissue inhibitor of metalloproteinase-2, MyoD, Myf5, MyoG and MyHC relative mRNA levels. The levels of the myostatin-1 and myostatin-2 genes were downregulated, and the protein expression levels of p-Smad2, Smad2, Smad4, p-Akt, Akt, LARP6 and Smad3 were increased.

Conclusions

The appropriate levels of dietary protein promoted the growth of sub-adult grass carp and improved muscle hardness by promoting the growth of muscle fibers, improving collagen synthesis and depressing collagen degradation. In addition, the dietary protein requirements of sub-adult grass carp were 26.21% and 24.85% according to the quadratic regression analysis of growth performance (SGR) and the muscle hardness (collagen content), respectively.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40104-022-00747-7.

Dietary isoleucine affects muscle fatty acid and amino acid profiles through regulating lipid metabolism and autophagy in hybrid catfish Pelteobagrus vachelli ♀ × Leiocassis longirostris ♂

The present study explored the impacts of Ile on muscle fatty acid and amino acid profiles, lipid metabolism, and autophagy in hybrid catfish. Seven isonitrogenous (387.8 g/kg protein) semi-purified diets were formulated to contain 5.0 (control), 7.5, 10.0, 12.5, 15.0, 17.5, and 20.0 g Ile/kg diet respectively. The fish (initial weight of 33.11 ± 0.09 g) were randomly assigned to 7 groups for a 56-day trial. Each group has 3 replicates with 30 fish per replicate, fed at 08:00 and 18:00 each day. Results showed that muscle protein and lipid, C14:0, C18:0, C22:0, C14:1, C18:1n-9, polyunsaturated fatty acid (PUFA), Arg, Ile, Ala, Cys, Gly, Tyr, essential amino acid (EAA), and total amino acid (TAA) contents and flavor amino acid (FAA)/TAA in muscle had positive linear and/or quadratic responses to dietary Ile levels (P < 0.05). Fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD), acetyl-CoA carboxylase (ACC), and lipoprotein lipase (LPL) activities had positive linear and/or quadratic responses, but carnitine palmitoyl transferase 1 (CPT1) activity had a negative response with increasing dietary Ile levels (P < 0.05). The mRNA expressions of FAS, SCD, ACC, LPL, fatty acid binding protein 4 (FABP4), FATP1, sterol response element-binding protein 1c (SREBP-1c), sequestosome 1 (SQSTM1), and adenosine 5′-monophosphate-activated protein kinase (AMPK) had positive linear and/or quadratic responses to dietary Ile levels (P < 0.05). The mRNA expressions of hormone-sensitive lipase (HSL), CPT1, peroxisome proliferator-activated receptor α (PPARα), PPARγ, uncoordinated 51-like kinase 1 (ULK1), beclin1 (Becn1), autophagy-related protein 9α (Atg9α), Atg4b, Atg7, autophagy marker light chain 3 B (LC3B), and SQSTM1 in muscle had negative linear and/or quadratic responses to dietary Ile levels (P < 0.05). The p-AMPK and ULK1 protein levels, and p-AMPK/AMPK were decreased by 12.5 g Ile/kg in the diet (P < 0.05). Finally, SQSTM1 protein level had the opposite effect (P < 0.05). The above results indicate that dietary Ile improves fish muscle fatty acid and amino acid profiles potentially via respectively regulating lipid metabolism and autophagy. The Ile requirement of hybrid catfish (33 to 72 g) were estimated to be 12.63, 13.77, 13.75, 11.45, 10.50, 12.53 and 12.21 g/kg diet based on the regression analysis of protein, lipid, SFA, PUFA, FAA, EAA, and TAA muscle contents, respectively.

Effects of Restricted Feeding on Growth Performance, Intestinal Immunity, and Skeletal Muscle Development in New Zealand Rabbits

Simple Summary

The high prevalence of gastrointestinal diseases in young rabbits is the major cause of impediment in the development of the rabbit industry. Presently, few companies have adopted methods of restricting feeding to improve the survival rate independent of the effect on their growth and development. To explore the effects of different feeding-restriction levels on the growth performance, intestinal immunity, and skeletal muscle development of meat rabbits, 198 New Zealand meat rabbits of 35 days old were selected and randomly divided into three groups: (1) a control group, (2) a 15% feeding restriction group, and (3) a 30% feeding restriction group, with 66 in each group with an equal number of males and females. The growth performance measurement and health-risk assessment indicators, measurement of digestive enzyme activity, immune and antioxidant indexes, and regulation mechanism were evaluated and explored. Finally, we found that a 30% feeding limit affected the growth and development of skeletal muscle in growing rabbits by regulating the PI3K/Akt signaling pathway.

Abstract

This study aimed to explore the effects of different feeding restriction levels on the growth performance, intestinal immunity, and skeletal muscle development of meat rabbits. Additionally, we studied whether complete compensatory growth could be obtained post 2 weeks of restricted feeding, in order to seek a scientific mode of feeding restriction. Each of three groups was exposed to 3 weeks of feeding restriction and 2 weeks of compensatory growth. The 15% feeding restriction showed a negligible effect on the final body-weight of the rabbits (p > 0.05), but significantly reduced the feed-to-weight ratio (p < 0.05); reduced diarrhea and mortality; and increased digestive enzyme activity and antioxidant capacity. However, a 30% feeding-restriction level substantially reduced the growth rate of the rabbits (p < 0.05), impaired skeletal muscle development, and showed no compensatory growth after 2 weeks of nutritional recovery. Additionally, immunoglobulin and antioxidant enzyme synthesis were impaired due to reduced nutritional levels, and levels of pro-inflammatory factors were increased during the compensation period. The IGF1 mRNA expression decreased significantly (p < 0.05), whereas MSTN and FOXO1 expression increased noticeably (p < 0.05). Moreover, protein levels of p-Akt and p-p70 decreased significantly in the 15% feeding restriction group. Overall, the 15% feeding limit unaffected the weight and skeletal muscle development of rabbits, whereas the 30% feeding limit affected the growth and development of skeletal muscle in growing rabbits. The PI3K/Akt signaling pathway is plausibly a mediator of this process.