Formation of Intermediate Amylose Rice Starch-Lipid Complex Assisted by Ultrasonication

Chain length of fatty acid determines the reassembly behaviors of starch-lipid complexes following microwave heat-moisture treatment

Food postprocessing can induce the structural changes of starch-lipid complexes, however, how the chain length of fatty acids affects their reassembly behaviors during postprocessing has not been researched. Accordingly, starch-lipid complexes containing varying chain lengths of fatty acids were prepared and the changes in their structures and digestibility were investigated during microwave heat-moisture treatment. After treatment, the contents of complexed lipids, complex index, and single helix in the complexes increased, and the values were lower for complexes containing longer-chain fatty acids. Although more single helices formed for short-chain fatty acids (10 ≤ C ≤ 12), the short-range molecular order and relative crystallinity of the complexes decreased. However, the complexes containing long-chain fatty acids (14 ≤ C ≤ 18) showed the opposite changes. The relative crystallinity of treated samples increased (from 12.0 % to 20.1 %) with increasing chain length of the fatty acids. Moreover, the treated samples exhibited greater enzyme resistance.

Debranching by enzymatic extrusion of oat flour for enhanced amylose-lipid complex formation: Effects on in vitro digestibility and functional properties

The amylose-lipid complex, also known as resistant starch type 5, is classified as dietary fibre with well-recognized health benefits. This study investigated its formation in pre-gelatinized whole oat flour using enzymatic extrusion-debranching and evaluated its effects on in vitro digestibility and functional properties. Whole oat grains were cooked in a steam oven, dried, ground, blended with pullulanase (60 U/g), and extruded enzymatically. Enzymatic extrusion increased oat flour's amylose content from 16.71 % to 26.93 % and resistant starch from 6.87 % to 31.99 %. Enzyme-extruded oat flour exhibited a V-type crystallinity pattern, confirmed amylose-lipid complex formation, and showed good thermal stability with two endothermic peaks at 90-110 °C and 110-130 °C. Additionally, enzymatic extrusion reduced the flour's viscosity and increased the water solubility index. These findings confirm that pullulanase extrusion effectively enhances resistant starch in lipid-rich cereal flour.

Formation and in vitro starch digestibility of amylose-lipid complex using cooked rice starch and an emulsified formulation

This study aimed to investigate amylose-lipid complex (ALC) formation and starch digestibility in cooked rice starches (CRSs) with the addition of 0, 5, and 10 % emulsified formulation (EMF). The addition of EMF did not affect the content of non-starch lipids but tended to increase the content of total lipids and starch lipids. The absorption rate of 995 cm-1/1022 cm-1 of CRSs increased with the addition of EMF, while that of 1047 cm-1/1022 cm-1 remained unchanged regardless of the addition of EMF. Compared to CRSs without EMF, CRSs with EMF were observed as thin, rounded, and amorphous with depressions. The addition of more than 5 % EMF decreased the rapidly digestible starch content, the equilibrium concentration of starch hydrolysis, and the estimated glycemic index of CRSs; increased the resistant starch content and particle size; and did not change the apparent viscosity.

Starch-lipid complexes and their application: A review

The starch-lipid complexes have recently attracted extensive interest due to their excellent properties, such as the decrease of digestibility and the inhibition of starch gelatinization and retrogradation. The review discussed the formation, structure, functionalities and preparation methods of starch-lipid complexes, and most importantly, their application. The starch-lipid complex is classified as a new type of resistant starch-RS5, which can reduce postprandial blood glucose response and regulate human gut health. Over the past few years, starch-lipid complexes have been increasingly reported for applications in food additives, fat substitutes and carriers of nutrients and medicine, regulation of intestinal flora and production of food packaging films. A comprehensive review of applications of starch-lipid complexes is of great importance for understanding and expanding the application of complexes. But the regulatory mechanism of starch-lipid complexes on food quality, food packaging films and intestinal flora is still unclear, which deserves further study in the future. Targeted medicine delivery using starch-lipid complexes may be also a promising and challenging direction in the future.

Rice flour-based filled hydrogel: an effective vitamin D encapsulation system as influenced by rice flour variety

This study investigated the effects of the physicochemical properties of filled hydrogels based on rice flour with varying amylose contents on the stability of encapsulated vitamin D3 (VD, cholecalciferol). The filled hydrogel, prepared based on Saemimyeon with an amylose content of 25.5%, formed a gel with strong elasticity, showing the highest stability during in vitro digestion, as well as excellent pH and storage stability of the encapsulated VD. Dodamssal, which had the highest amylose content (> 40%) and gelatinization temperature, retrograded rapidly due to its high leached amylose content. This phenomenon caused gel shrinkage and subsequent emulsion leakage, resulting in a relatively lower VD retention rate after in vitro digestion compared to the Saemimyeon-based filled hydrogel. Nevertheless, compared to the emulsion system, the rice flour-based filled hydrogels formed various types of gel matrices that provided a physical barrier to the VD-containing lipid droplets, thereby significantly protecting them from the external environment.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-024-01806-7.

Reduction of oil absorption and acrylamide content in banana slices by infrared frying

BACKGROUND

The crust characteristics of fried crisps determine their oil absorption. Starch structures, as the main components of fried starchy fruits and vegetables, influence their crust formation and properties. This study investigated the reduction of oil uptake and acrylamide content in infrared-fried (IF) banana slices by modifying starch structures at varying infrared power levels.

RESULTS

Infrared heating improved heat transfer and surface moisture removal in fried banana slices. It facilitated crust formation in the IF samples and produced increased crust uniformity, crust ratio, and hardness. Analysis of the porous properties showed that the volume fraction of pores sized 100-250 μm was reduced in IF samples but the proportion of pores with a diameter ranging from 0.02 to 10 μm was increased. Infrared frying reduced the total oil uptake, surface oil, and structural oil content in banana slices, and each of these measures decreased as infrared power levels increased. Characterization of the starch structures suggested that the damage to the crystalline structure was increased in IF samples and more starch-lipid complexes were generated, which would be responsible for the formation of a denser and thicker crust. The acrylamide content in the IF sample was reduced, as determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

CONCLUSION

Modifications to starch structures (crystalline structures and chemical structures) play a crucial role in oil absorption in fried starchy fruits and vegetables. Infrared frying can be used as an alternative method to produce low-fat fruits and vegetable crisps with reduced acrylamide content. © 2024 Society of Chemical Industry.

Effects of different fatty acids on the structure, physicochemical properties, and in vitro digestibility of Chinese yam resistant starch-lipid complexes

Nine CYRS-FA complexes were prepared by resistant starch in Chinese yam (CYRS) and nine fatty acids (FAs) with different chain lengths and degrees of unsaturation. CYRS-myristic acid and CYRS-palmitic acid showed higher complexing index (CI) and relative crystallinity (RC); CYRS-myristic acid and CYRS-oleic acid exhibited lower estimated glycemic index (eGI). Chain lengths of FAs showed significantly positive correlations with CI and contact angle (CA), and yet, unsaturation degree of FAs was negative correlated with both CI and CA. The eGI exhibited positive relations with solubility, and negative correlations with CI and RC. Therefore, the results indicated that chain lengths and unsaturation degrees of FAs were key factors for complexation of the CYRS-FA complexes, which influenced the structural, physicochemical and digestive properties. The findings were expected to provide a theoretical foundation for the interactions between starch and lipids in food processing, and elevate the high-tech values of Chinese yam.

Structural characteristics determining starch digestibility in cooked rice complexed with an emulsion formulation

To evaluate the effects of structural characteristics on amylose-lipid complex (ALC) formation and the starch digestibility of cooked rice grains with the addition of 0, 5, 10, and 20 % emulsification formulation (EMF), both cooked rice (CR) grains with intact structural characteristics and CR slurries with their structural characteristics destroyed were examined. When EMF was added, the surface firmness, adhesiveness and adhesion of the CR grain changed. Depressions associated with ALC formation were observed on the surface of CR grains. The addition of more than 10 % EMF significantly suppressed starch hydrolysis in CR grains, while there was no significant difference in the starch digestibility of CR slurries, regardless of the amount of EMF. These results revealed that the structural characteristics of a layer like ALC on the CR grains suppressed starch digestibility and that once the structural characteristics were destroyed, the inhibitory effect of ALC on starch digestibility was lost.

Preparing water-resistant films using partially debranched potato starch and oleic acid

Improvement in film-forming properties of starch is critical for the wide application of environmentally friendly starch film. To enhance moisture barrier and mechanical properties of starch films, the formation of starch-lipid inclusion complex was promoted by partial debranching of starch and reaction at various temperature. The partially debranched potato starch was initially prepared with pullulanase, and the starch-lipid inclusion complex was subsequently produced with oleic acid at various reaction temperatures of 30, 50, and 70 °C. The partial debranching combined with oleic acid addition induced characteristic V-type crystalline peaks in the X-ray diffraction (XRD) patterns. The highest reaction temperature, of 70 °C, induced more apparent XRD peaks and higher thermal transition temperatures and enthalpy. The partially debranched starch film with oleic acid at 70 °C showed a smooth and uniform surface with a more rigid and condensed network. The high content of starch-lipid inclusion complexes in a partially debranched starch film with oleic acid at 70 °C significantly reduced water vapor permeability (from 162.22 to 65.99 g∙mm∙m-2∙day-1∙atm-1) and increased both the contact angle (from 61.08 to 74.55°) and tensile strength (from 2.126 to 5.473 MPa) compared to a native starch film. Therefore, the formation of more abundant starch-lipid inclusion complexes at relatively high reaction temperatures with partial debranched starch can effectively enhance the moisture barrier properties of starch films for industrial application as biodegradable film.

Impact of Ultrasonic-Assisted Preparation of Water Caltrop Starch-Lipid Complex: Structural and Physicochemical Properties

This study investigates the effect of ultrasonic-assisted preparation on the structural and physicochemical properties of water caltrop starch-palmitic acid complexes as a function of ultrasound intensity and treatment time. All samples exhibited the characteristic birefringence of starch-lipid complexes under the polarized microscope, and flake-like and irregular structure under scanning electron microscope (SEM), indicating the formation of complexes through ultrasonic-assisted preparation. X-ray diffraction pattern further confirmed the transition from the original A-type structure for native starch to V-type structure for starch-lipid complexes, and the relative crystallinity of starch-lipid complexes increased as the ultrasound intensity and treatment time increased. Attenuated total reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR) analysis indicated a decreasing trend in absorbance ratio at wavenumber of 1022 cm-1/995 cm-1, suggesting that the increase in the complex promoted the self-assembly within the short-range ordered structure, leading to the formation of bonds between the complexes. However, rapid-visco analysis (RVA) demonstrated that the viscosity generally decreased as the ultrasound intensity and treatment time increased, possibly due to the reduction in molecular weight by ultrasound. Differential scanning calorimetric (DSC) analysis revealed that the control starch-lipid complex without ultrasound treatment (US-0-0) exhibited two distinct endothermic peaks above 90 °C, representing Type I (95-105 °C) and Type II (110-120 °C) V-type complexes. However, ultrasound-treated samples showed only one peak around 95-105 °C and increased enthalpy (∆H), which was likely due to the breakdown of amylose and amylopectin, leading to more complex formation with palmitic acid, while the resulting shorter chains in the ultrasound-modified sample favor the formation of Type I complexes.

Optimization of ultrasound-assisted extraction of mango cotyledon starch: Physicochemical, structural, thermal and functional properties

Mango (Mangifera indica L.) seed, a byproduct of mango pulp and juice processing, is recognized for its abundant starch content. The advancement of the modern food industry has prompted a shift away from traditional starch extraction methods due to their environmental impact and low efficiency. The study aimed to optimize the ultrasound-assisted extraction process of starch from the cotyledons of mango seeds, employing response surface methodology with a customized optimal design and an optimal-I optimality criterion. We investigated the effects of cotyledon/water ratio, time, power, and sonication frequency on maximizing starch extraction yield. We explored the impact of ultrasound on structural, morphological, functional, and pasting properties. The maximum starch extraction yield was 50.74%. This yield was about 82.4% higher than that of conventional wet extraction. Ultrasound-assisted extraction increased starch purity and amylose content; it reduced granule size while enhancing all starch pasting properties without affecting starch's chemical structure and morphological, thermal, and functional properties. The mango cotyledon starch can be classified as medium to normal amylose content starches, exhibiting A-type polymorphs, fast-swelling, and capable of forming strong, firm, low-sticky gels. These results demonstrate the potential applications of mango residue and ultrasound technology in the food and pharmaceutical industry.

Cutting-edge progress in green technologies for resistant starch type 3 and type 5 preparation: An updated review

Resistant starch (RS) is a dietary fiber that resists starch hydrolysis in the small intestine, and is fermented in the colon by microorganisms. RS not only has a broad range of benefits in the food and non-food industries but also has a significance impact on health promotion and prevention of non-communicable diseases. RS types 3 and 5 have been the focus of research from an environment-friendly perspective. RS3 is normally formed by recrystallization after physical modification, whereas RS5 is obtained by the complexation of starch and fatty acids through the thermomechanical methods. This review provides updates and approaches to RS3 and RS5 preparations that promote RS content based on green technologies. This information will be useful for future research on RS development and for identifying preparation methods for functional food.

Effect of ultrasound-pretreated starch on the formation, structure and digestibility of starch ternary complexes from lauric acid and β-lactoglobulin

Starch, lipids, and proteins are key macronutrients in starchy foods. Their interactions during processing can form starch-lipid-protein ternary complexes, significantly affecting food quality. Ultrasonic treatment, as a common processing method, is expected to regulate the quality of starchy foods by influencing the formation of ternary complexes. This study aimed to understand the effect of ultrasonic pretreatment on the formation of starch-lipid-protein ternary complexes using various types of starches. Wheat starch (WS), maize starch (MS), and potato starch (PS) were gelatinized and treated with ultrasound at various power densities (0-40 W/L) to form complexes with lauric acid (LA) and β-lactoglobulin (βLG), respectively. Ultrasound increased the amylose content of gelatinized WS, MS, and PS and shifted their chain length distribution towards the short chains. Results from Fourier transform infrared spectroscopy, laser confocal micro-Raman, X-ray diffraction, and differential scanning calorimetry showed that the largest amount of WS-LA-βLG complexes was formed at the ultrasonic power density of 10 W/L, and MS-LA-βLG and PS-LA-βLG complexes at 20 W/L. Additionally, ultrasound enhanced the content of resistant starch (RS) in the starch-LA-βLG complexes. The RS content increased from 14.12 % to 18.31 % for WS-LA-βLG, and from 19.18 % and 20.69 % to 27.60 % and 28.63 % for MS-LA-βLG and PS-LA-βLG complexes, respectively. This study presents an approach for facilitating the formation of ternary complexes, contributing to the development of low-GI functional foods.

Recent advancements in functionality, properties, and applications of starch modification with stearic acid: A review

Starch modifications using chemicals are widely used to improve the desirable properties of native starch. Starch modified with steric acid characterized the starch properties due to the formation of starch-steric acid complex. Structural and functional characteristics of modified starch are influenced by duration, starch-acid concentration ratio, and temperature during the reaction. The diffraction patterns of the starch-stearic acid complexes show a mixture of A-type/B-type and V-type patterns. Starch-stearic acid complexes are regarded as "Generally Recognized as Safe (GRAS)" and are thermally stable and exhibit high paste viscosity and non-gelling properties. Due to their reduced gelling ability and increased viscosity, they can be utilized as fat replacers. Starch stearate also has promising applications in drug delivery due to its biocompatibility and non-gelling properties, which can be utilized for controlled release systems. Additionally, its biodegradability and enhanced thermal stability make it an ideal candidate for use in environmentally friendly, biodegradable materials. Complexes also have the potential for food packaging applications due to their increased thermal stability and improved barrier properties due to the replacement of the hydroxyl group of starch with a hydrophobic functional group of stearic acid (SA). This review paper examines the reaction parameters involved in the SA modification of starches and explores the starch-SA complexes' impact on physicochemical factors, as well as key structural attributes and industrial applications.

Effect of electron beam irradiation pretreatment and different fatty acid types on the formation, structural characteristics and functional properties of starch-lipid complexes

The effects of different electron beam irradiation doses (2, 4, 8 KGy) and various types of fatty acids (lauric acid, stearic acid, and oleic acid) on the formation, structure, physicochemical properties, and digestibility of starch-lipid complex were investigated. The complexing index of the complexes was higher than 85 %, indicating that the three fatty acids could easily form complexes with starch. With the increase of electron beam irradiation dose, the complexing index increased first and then decreased. The highest complexing index was lauric acid (97.12 %), stearic acid (96.80 %), and oleic acid (97.51 %) at 2 KGy radiation dose, respectively. Moreover, the microstructure, crystal structure, thermal stability, rheological properties, and starch solubility were analyzed. In vitro digestibility tests showed that adding fatty acids could reduce the content of hydrolyzed starch, among which the resistant starch content of the starch-oleic acid complex was the highest (54.26 %). The lower dose of electron beam irradiation could decrease the digestibility of starch and increase the content of resistant starch.

Comparative study on the structure characterization and activity of RS5 made from Canna edulis native starch and high-amylose corn starch

In this study, the high amylose corn starch and Canna edulis native starch were compounded with lauric acid and fermented by human fecal inoculation in vitro. Changes in beneficial metabolite profile and microbiota composition were evaluated. The structural properties showed that both NS-12C and HAMS-12C formed V-shaped crystals under the same preparation method, but NS-12C had a higher composite index and resistance content than HAMS-12C. At the end of fermentation, the starch-lauric acid complexes prepared from the two types of starch significantly promoted the formation of short-chain fatty acids and the contents of acetic acid, butyric acid and valeric acid produced by NS-12C were higher than those of HAMS-12C(p>0.05). HAMS-12C and NS-12C both increased the relative abundance of Blautia. Notably, NS-12C also increased the relative abundance of beneficial bacteria Bifidobacterium and Meganomas, while HAMS-12C did not. These results suggested that this effect may be related to starch type and provide a basis for designing and producing functional foods to improve intestinal health in Canna edulis native starch.

Functionalization Methods of Starch and Its Derivatives: From Old Limitations to New Possibilities

It has long been known that starch as a raw material is of strategic importance for meeting primarily the nutritional needs of people around the world. Year by year, the demand not only for traditional but also for functional food based on starch and its derivatives is growing. Problems with the availability of petrochemical raw materials, as well as environmental problems with the recycling of post-production waste, make non-food industries also increasingly interested in this biopolymer. Its supporters will point out countless advantages such as wide availability, renewability, and biodegradability. Opponents, in turn, will argue that they will not balance the problems with its processing and storage and poor functional properties. Hence, the race to find new methods to improve starch properties towards multifunctionality is still ongoing. For these reasons, in the presented review, referring to the structure and physicochemical properties of starch, attempts were made to highlight not only the current limitations in its processing but also new possibilities. Attention was paid to progress in the non-selective and selective functionalization of starch to obtain materials with the greatest application potential in the food (resistant starch, dextrins, and maltodextrins) and/or in the non-food industries (hydrophobic and oxidized starch).

Preparation, structure, and in-vitro hypoglycemic potential of debranched millet starch-fatty acid composite resistant starch

Currently, the preparation methods and basic physicochemical properties of starch-FA complexes have been widely studied; however, no in-depth research on the regulatory mechanism of the digestive properties of debranched starch-unsaturated FA complexes has been conducted. Therefore, six fatty acids with different carbon chains and different degrees of unsaturation were complexed with de-branched millet starch in this research, using the microwave method. Microwave millet starch-linoleic acid complex (MPS-LOA) had the highest resistant starch (RS) content, and the structure and physicochemical properties of MPS-LOA were determined using various molecular techniques. The results indicate that MPS-LOA had a resistant starch (RS) content of 40.35% and the most notable fluorescence. The characteristic UV peaks of MPS-LOA were blue-shifted, and new IR peaks appeared. The crystalline structure changed to V-type crystals, the crystallinity increased, and the molecular weight decreased. The enthalpy and coagulability of MPS-LOA increased, and the swelling force decreased. Additionally, MPS-LOA showed enhanced α-glucosidase and α-amylase inhibition, and in-vitro hydrolysis kinetics analysis of MPS-LOA showed a hydrolysis index of 53.8 and an extended glycemic index (eGI)I of 54.6, indicating a low eGI food suitable for consumption by people with type II diabetes. These results provide a theoretical basis for the preparation of amylopectin- and starch-based foods with an anti-enzyme structure and a low glycemic index (GI).

Preparation of the starch-lipid complexes by ultrasound treatment: Exploring the interactions using molecular docking

In this work, Corn Starch (CS)-Lauric acid (LA) complexes prepared by different ultrasound times were explored for multi-scale structure and digestibility. The results showed that the average molecular weight of the CS decreased from 380.478 to 323.989 kDa and the transparency increased to 38.55 % after 30 min of ultrasound treatment. The scanning electron microscope (SEM) results revealed a rough surface and agglomeration of the prepared complexes. The complexing index of the CS-LA complexes increased by 14.03 % compared to the non-ultrasound group. The prepared CS-LA complexes formed a more ordered helical structure and a more dense V-shaped crystal structure through hydrophobic interactions and hydrogen bonding. In addition, fourier transforms infrared spectroscopy and the molecular docking revealed that the hydrogen bonds formed by CS and LA promoted the formation of an ordered structure of the polymer, retarding the diffusion of the enzyme and thus reducing the digestibility of the starch. With correlation analysis, we provided insight into the multi-scale structure-digestibility relationship in the CS-LA complexes, which provided a basis for the relationship between structure and digestibility of lipid-containing starchy foods.

Comparative Evaluation of Hydrothermally Produced Rice Starch-Phenolic Complexes: Contributions of Phenolic Type, Plasma-Activated Water, and Ultrasonication

A thorough investigation of the viability of rice starch conjugation with three different phenolic compounds-gallic acid, sinapic acid, and crude Mon-pu (Glochidion wallichianum Muell Arg) (MP) extract-was conducted using a variety of developed methods which modified the techno-functionality and digestibility of the end product. With and without the aid of ultrasonication (US), phenolic compounds were complexed with hydrothermally pre-gelatinized rice starch prepared using distilled water or plasma-activated water (PAW). The in vitro digestibility, structural features, rheological and thermal properties, and in vitro antioxidant activity of starch-phenolic complexes were evaluated. The US-assisted starch-MP complex in water had the highest complexing index (CI) value (77.11%) and resistant starch (RS) content (88.35%), resulting in a more compact and stable ordered structure. In all complexes, XRD revealed a new minor crystalline region of V-type, which was stabilized by hydrogen bonding as defined by FTIR and H¹-NMR. Polyphenols caused a looser gel structure of starch, as imaged by a scanning electron microscope (SEM). Starch-phenolic complexes outperformed other complexes in terms of in vitro antioxidant activity. Gallic acid addition to starch molecules boosted DPPH scavenging activity, notably when synthesized in PAW regardless of US assistance, although having lower CI and RS values than the MP complex. Therefore, this research lays the groundwork for the efficient production of functional food ingredients based on rice starch and polyphenols.

Biopreservation of Refrigerated Mackerel (Auxis thazard) Slices by Rice Starch-Based Coating Containing Polyphenol Extract from Glochidion wallichianum Leaf

Both microbial decomposition and oxidative deterioration contribute to the qualitative degradation of fresh or minimally preserved fish, which negatively impacts the shelf-life of fish, especially those with dark flesh like mackerel. It is becoming more typical to use edible coatings to preserve the freshness of fish products. Herein, the effects of a rice starch (RS) based coating incorporated with dried crude, aqueous Mon-pu (Glochidion wallichianum) leaf extract (MPE) at varying concentrations (0, 0.02, 0.1, 0.5, and 1.0% w/w) on the quality characteristics of mackerel (Auxis thazard) slices during storage at 4 °C were investigated. Uncoated slices had a shelf-life of 6 days, whereas samples coated with RS and 0.5% MPE extended the shelf-life to 9 days by keeping the overall microbiological quality below the permitted level of 6 log CFU/g. The changes in thiobarbituric acid reactive substances (TBARS; <2 mg malondialdehyde equivalent/kg), propanal content, heme iron degradation, myoglobin redox instability, and surface discoloration (a* value and total color difference; ΔE) can all be delayed by this coating condition. Additionally, the RS-MPE coating can maintain the sensory quality of refrigerated mackerel slices and preserve the textural property (water holding capacity and hardness), as well as postpone the development of an off-odor as indicated by lowered contents of total volatile base-nitrogen (TVB-N; not exceeding the acceptable limit of 25 mg/100 g) and trimethylamine (TMA; not exceeding the acceptable limit of 10 mg/100 g). Therefore, a biopreservative coating made of RS and MPE, especially at 0.5%, can be employed to extend the shelf-life of refrigerated mackerel slices up to 9 days.