Recent trends and applications of cellulose nanocrystals in food industry

Trends in Food Science & Technology 93 (2019) 136–144

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Trends in Food Science & Technology journal homepage: www.elsevier.com/locate/tifs

Recent trends and applications of cellulose nanocrystals in food industry a,1

Ruojun Mu , Xin Hong Yafeng Zhenga,∗∗ a b c

a,1

a

a

a

b

T

c,∗

, Yongsheng Ni , Yuanzhao Li , Jie Pang , Qi Wang , Jianbo Xiao ,

College of Food Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China Institute of Agricultural Engineering, Fujian Academy of Agricultural Sciences, Fuzhou, 350003, China International Research Center for Food Nutrition and Safety, Jiangsu University, Zhenjiang, 212013, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Cellulose nanocrystals Food industry Food packaging Functional food Food safety

Background: The development of nanomaterials with edible and biodegradable properties is now an urgent need of food science and technology. The application of nanomaterials in the food production, processing and packaging promotes the development of a novel technology - food nanotechnology. Scope and approach: Cellulose nanocrystals are nanoscale celluloses extracted from natural fibers and organized in a structure of strongly ordered crystalline particles. In this review, recent developments in advantages and safety issues of cellulose nanocrystal, as well as its applications in food industry, such as biodegradable packaging, delivery systems, food stabilizer and functional food ingredients were highlighted. Key findings and conclusions: The cellulose nanocrystals have excellent physical and chemical properties and are considered as novel food ingredients and biodegradable packaging materials in food industry. Based on its small size, large surface area, high crystallinity and high Young's modulus, cellulose nanocrystals exhibited excellent mechanical properties, high thermal stability, active chemical reaction properties, and the rheological properties of shear thinning. Cellulose nanocrystals can be used as a low calorie replacement for carbohydrate additives used as thickeners, flavor carriers and suspension stabilizers in a wide variety of food products. Cellulose nanocrystals showed excellent functions in application of delivery system, which make it an ideal candidate to protect nutrients and active ingredients in food products.

1. Introduction Cellulose, a macromolecule polysaccharide consisting of glucose, is the most widely distributed and most abundant polysaccharide in nature, accounting for more than 50% of the carbon content in the plant community (Klemm, Heublein, Fink, & Bohn, 2005). Nanocellulose is a term referring to nano-structured cellulose (Morán, Alvarez, Cyras, & Vázquez, 2008). This may be either cellulose nanofibers (CNF) also called microfibrillated cellulose (MFC), cellulose nanocrystals (CNC), or bacterial nanocellulose (BNC), which refers to nano-structured cellulose produced by bacteria (Lin & Dufresne, 2014). CNF, diameter of about 5–7 nm and a length of hundreds nm, is composed of nanocelluloses with alternating crystalline and amorphous domains with soft and long chain structures. CNF has high-aspect-ratio fibrils that for strong and entangled networks. With microscopic observations and light scattering techniques, CNC can be evaluated as elongated rod-like nanoparticles, since the amorphous domains have been degraded during the

hydrolysis. Each rod of CNC can be considered as a rigid cellulosic crystal. In recent years, unique functions of CNC have been found by scientists such as excellent mechanical properties (Kamal & Khoshkava, 2015), self-assemble abilities (Hsieh, 2013), thixotropic function (Buchanan, Knaapila, Helgesen, & Hoeyer, 2013), chemical reactivity (Tao et al., 2002), surface interface effect (Routara, Bandyopadhyay, & Sahoo, 2009) and photonic properties (Guidetti, Atifi, Vignolini, & Hamad, 2016). The nanocellulose was first used in the late 1970s to describe a product prepared as a gel type material by passing wood pulp through a Gaulin type milk homogenizer at high temperature (Turbak, Snyder, & Sandberg, 1983). To date, many different types of nanocellulose have been obtained including CNF, CNC, and BNC (Gatenholm & Klemm, 2010; Peng, Dhar, Liu, & Tam, 2011; Zhang et al., 2013). CNC can be obtained from native fibers by an acid hydrolysis, giving rise to highly crystalline and rigid nanoparticles which are shorter than the nanofibrils obtained through homogenization, microfluiodization or

∗

Corresponding author. Corresponding author. E-mail addresses: [email protected] (J. Xiao), zyff[email protected] (Y. Zheng). 1 These authors contributed equally to this work and should be considered as co-first authors. ∗∗

https://doi.org/10.1016/j.tifs.2019.09.013 Received 30 December 2018; Received in revised form 18 August 2019; Accepted 13 September 2019 Available online 15 September 2019 0924-2244/ © 2019 Elsevier Ltd. All rights reserved.

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grinding routes (Vilarinho, Silva, Vaz, & Farinha, 2017). CNC has been studied for decades and recently developed a wide array of uses in various fields and applications (Cao, Dong, & Li, 2007; Dong & Roman, 2007; Samir, Alloin, Sanchez, & Dufresne, 2004). CNC can be modified to meet new specifications required to enhance products or to generate completely new applications that were previously thought impossible (Salajková, Berglund, & Zhou, 2012). In food industry, consumers are demanding ever increasing quality in food and beverage products. CNC can be a component in developing healthy, sustainable and safe food and beverages that appeal to ever more exacting customer needs (Julkapli & Bagheri, 2016). For instance, CNC can form stable emulsions which improved texture and suspension quality (Kalashnikova, Bizot, Cathala, & Capron, 2011). Meanwhile, this renewable nanomaterial has potential application in biodegradable packaging for food (Yu, Yan, & Yao, 2014). The aim of this review is to describe the properties and advantages of the CNC while focusing on its production and applications in food industry. Besides, the source and manufacture of CNC, and its safety issue in digesting system are presented and discussed.

and tightly packed film after drying (Risteen et al., 2017). 2) CNC is thixotropic that can give excellent processing and storage properties when added into fluid foods. Fluids containing CNC is shear thinning, meaning they decrease in viscosity with the application of shear. This property makes the fluid much easier for mechanical processing. Furthermore, CNC could act as a stabilizer during storage of the fluids as a high viscosity obtained without shearing (Khoshkava & Kamal, 2014; Wang, Drzal, Qin, & Huang, 2015). 3) CNC is chemically reactive and compatible with a wide range of solvents and polymer matrices, such as sulfuric acid and polyvinyl alcohol. (Buffa, Casado, Mucci, & Aranguren, 2019; Jiménez Saelices, Save, & Capron, 2019; Zhang, He et al., 2014). Hydroxyl groups presented in CNC chains develop the hydrogen bonds that give the CNC a reactive surface on two of the crystal's facets (Makarem, Lee, Sawada, O'Neill, & Kim, 2017). Many microencapsulation processes have taken advantage from the CNC reactivity, which allows CNC binding with a variety of hydrophobic structures (Huq et al., 2014, 2016; Yoo, Martinez, & Youngblood, 2017). All advantages of the CNC make it a useful material and/or ingredient to apply in the field of food science and engineering.

2. Advantages of CNC

3. Preparation of CNC

Cellulose is the most widely distributed and most abundant polysaccharide in nature (Wang, Wang, Jin, Wang, & Jin, 2011). CNC is produced by revealing basic structural building blocks of cellulose through various processing methods (Habibi, Lucia, & Rojas, 2010). Fig. 1 illustrates the schematic of CNC extraction from plant fibers. The final morphology and properties of CNC depend on the raw materials used and the process for production. 1) CNC exhibits strong mechanical properties and high surface. In concentrated suspensions, CNC was arranged as a chiral nematic liquid crystal, which creates a hard, smooth

One of the most key reasons why CNC has gotten so much concern in industry is its wide distribution in natural resources (Natterodt, PetriFink, Weder, & Zoppe, 2017). Among all, agro wastes are main sources of CNC. It not only makes this nanocrystal one of the cheapest material, but also motivates the agro wastes recycled to reduce the environment pollution. The most popular method to prepare CNC is acid hydrolysis, and recently combined with several different mechanical treatments, such as ultrasonic homogenization, smash after freeze drying, and colloid grinding. (Abdallah & Kamal, 2018; Lee, Shin, & Park, 2017).

Fig. 1. Schematic of CNC extraction from plant fibers. a) Agricultural products or wastes are used as sources for CNC; b) Cellular walls containing NC for further process; c) cellulose fibrils obtained from cellular walls; d) individual cellulose fibrils are further prepared by multiple mechanical shearing actions; e) Cellulose molecule, Chemically induced destructuring strategy, such as acid hydrolysis, is commonly performed for the extraction of CNC from native cellulose; f) AFM image shows nanostructures of CNC. 137

Spherical size of 58–96 nm.

Length of 160 ± 20 nm. Diameter of 4.5 ± 1 nm. Mean equivalent spherical diameter of 130 nm.

Average diameter of 9.1 ± 3.1, 7.6 ± 3.4 and 5.2 ± 2.9 nm and average length of 315.7 ± 30.3, 294.5 ± 29.1 and 285.4 ± 36.5 nm were measured for CNC. Diameter of 15–20 nm.

Average diameter of 95 ± 24 nm, up to 304 ± 71 nm. An average length of 122.66 ± 39.40 nm, a diameter of 2.77 ± 0.67 nm.

Average diameter in the range of 5–10 nm.

Garlic skin

Hemp fibers Mango seeds

Red algae waste

Sisal fibers Soy hull

Sunflower stalks

Rice straw

177 nm long (ranging from 161 to 193), 12 nm wide (ranging from 10 to 13).

Cotton

Length of 310 ± 160 nm. Width of 20 ± 4 nm.

Diameter and length in the range from 500 nm to 600 nm, and 70 nm–98 nm respectively. Particle size of 20 nm. Length of 80–500 nm. Widths of about 6 nm.

Bamboo pulp

Banana peel waste Coconut husk fibers Coffee husk

CNC Dimension

Source of agro waste

Reinforcing capacity with aspect ratio of > 10 larger aspect ratio, better dispersion and enhanced interface interaction spherical in shape with the size of 58–96 nm

Acid hydrolysis Melt-mixing

Steam explosion treatment and hydrolysis

Electrospinning Acid hydrolysis

Acid hydrolysis

Acid hydrolysis

Alkali treatment and acid hydrolysis Surfactant modified Acid hydrolysis improvement of barrier properties needle-shaped, with high crystallinity (90.6%), good thermal stability (around 248 °C) high mechanical performance and good transparency Enhanced storage modulus, tensile properties, and thermal stability stiffer mats and higher Tg values a high crystallinity (73.5%), an aspect ratio around 44 Enhanced thermal, mechanical and barrier properties

Hydrogen storage capacity, supercapacitance behavior Tensile of 120 MPa/kg m3 Aspect ratio of up to 60

Surface-modified magnetic Acid hydrolysis Sulfuric acid hydrolysis

Unique properties

Method (extraction/ modification)

Table 1 Production of CNC from different agro wastes with various properties (Produced from Collazo-Bigliardi, Ortega-Toro, and Chiralt 2018).

Luzi et al. (2016) Henrique, Silvério, Neto, and Pasquini (2013) El Achaby, Kassab, Aboulkas, Gaillard, and Barakat (2018) Boonterm et al., 2015; Kargarzadeh, Johar, & Ahmad, 2017 Santos er al. (2015) Flauzino Neto, Silvério, Dantas, and Pasquini (2013) Fortunati et al. (2016)

Collazo-Bigliardi, Ortega-Toro, and Chiralt (2018) Ludueña, Vázquez, & Alvarez, 2012; Morais, Rosa, and Souza Filho et al., 2013 Reddy and Rhim (2014)

Hossain, Ibrahim, and AlEissa (2016) Rosa et al. (2010)

Borkotoky, Dhar, and Katiyar (2018)

References

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Trends in Food Science & Technology 93 (2019) 136–144

Table 1 summarizes the production of CNC from different agro wastes, based on recent studies in cellulose science and engineering. Bacteria are another sources to produce CNC in substantial quantities (Shi, Zhang, Phillips, & Yang, 2014). CNC prepared from bacterial celluloses are considered as ‘green nanomaterials’, not only depending on their renewable nature, but also ease of production without the involvement of hazardous chemical treatments (George, Ramana, Bawa, & Siddaramaiah, 2011). Moreover, bacterial CNC is known to have better properties like crystallinity, water holding capacity, mechanical and thermal properties (Ullah, Santos, & Khan, 2016). There are many microbial strains that can synthesize bacterial cellulose, such as Acetobacterxylinum, Agrobacterium, Alcaligenes, Sarcina, and Rhizobium (ElSaied, Basta, & Gobran, 2004). 4. Applications of CNC in food industry

CNC has been reported to improve the mechanical properties of polymers, such as thermosetting resins (Giese, Khan, Hamad, & MacLachlan, 2013), starch-based matrixes (John & Thomas, 2008), soy protein (Li, Jin, Han, Li, & Chen, 2017), rubber latex (Harahap, Ridha, Halimatuddahliana, & Iriany, 2018), and poly(lactide) (Arias, Heuzey, Huneault, Ausias, & Bendahou, 2015). The composite applications may be for use as coatings and films in food packaging (Yu et al., 2014). Meanwhile, CNC is a dietary fiber extracted from edible products, which make a good candidate in functional foods as food additives (Hemmati, Jafari, Kashaninejad, & Motlagh, 2018). In particular, nanocellulose can be used as a low calorie replacement for carbohydrate additives as thickeners, flavor carriers and suspension stabilizers in a wide variety of food products (Dhar, Bhardwaj, Kumar, & Katiyar, 2014) and is useful for producing fillings, crushes, chips, wafers, soups, gravies, puddings etc. (Turbak, Snyder, & Sandberg, 1982). Fig. 2 demonstrates the main applications of CNC in food industry. In this section, we will detailedly explore the applications of CNC in food industry. 4.1. Biodegradable packaging composites

Packages play a key role in human daily life with their protection, communication and convenience for decades. Increasingly

Fig. 2. Application of CNC as (ingredients in) a) Biodegradable packaging composites; b) Delivery systems; c) Food stabilizers; d) Functional foods; and e) Starch foods.

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added, which represented less destruction of bacterial cell. Most importantly, it was found that the CNCs can improve the viability of the probiotics during storage and gastrointestinal simulation experiment. With 13% CNC added, the viability of L. rhamnosus in alginate microbeads were improved by 45% (25 °C) and 35% (4 °C) after 42 days’ storages. After 2 h exposure to SGF, alginate-CNC formulation improved the viability of L. rhamnosus by 41% (before freeze-drying) and 38% (after freeze drying) as compared to alginate microbeads alone.

environmental deterioration drives us to produce biodegradable materials (Malik, 2014). In food industry, packaging not only refer to protection and convenience, but also to increase the shelf life and nutrition capacity of food and communicate food quality to customers (Geueke, Groh, & Muncke, 2018). CNC is an ideal candidate to produce food packaging, based on its natural resources and high strength. For pure CNC film, the oxygen permeability was 17 ± 1 mLm−2/d with thickness of 21 ± 1 mm (Nair, Zhu, Deng, & Ragauskas, 2014). The excellent oxygen barrier properties of CNC are due to a combination of a high crystallinity, a network structure held together via strong interand intramolecular hydrogen bonds (Normand, Moriana, & Ek, 2014). As a key ingredient in food packaging, either original or functionalized CNC has been applied to composite with traditional polymers like poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) (Yu et al., 2012), poly vinyl alcohol (PVA) (George, Bawa, & Siddaramaiah, 2010), polylactide acid (PLA) (Fortunati et al., 2012), etc. to obtained many functions that not present in their pure states, such as excellent oxygen barrier, enhanced mechanical and biodegradable properties. The incorporation of CNC caused a significant stiffness increase at filler concentrations in the range of 1–10 wt% (Yu et al., 2013). For instance, a 250% increase in Young's modulus was obtained when CNC (10 wt%) was added to PHBV (Yu et al., 2012). While about 50% improvement in tensile strength was achieved by the addition of 4 wt% CNC to PVA (George et al., 2010). Surfactant-modified CNC (1 wt% and 5 wt%) were introduced to synthesize the PLA composite packing films, which got a better water permeability (reduction of 34%) and good oxygen barrier properties (Fortunati et al., 2012).

4.3. Food stabilizers Stability of processed food is always a core issue in food industry. Problems arising from many fluid products and fresh-made beverages are thinning and phase separation with elapse of time (Mutilangi & Pereyra, 2008). In this situation, after a relative long time storage, those products begin to thin and/or form a layer of water at the top or bottom, even they are still safe to consume. Therefore, it would be desirable to have a shelf-stable product which does not suffer from this disadvantage (Vaast, Bertrand, Perriot, Guyot, & Génard, 2006). Many kinds of stabilizers were developed to enhance the quality of the food products. Varieties of gums like xanthan gum (Kumar, Rao, & Han, 2018), carrageenan (Bahramparvar, Mazaheri Tehrani, & Razavi, 2013), gellan gum (Cropotova, Popel, & Parshakova, 2013) and locust bean gum (Murray & Phisarnchananan, 2016) were applied as stabilizers in food products based on their excellent emulsification and stabilization. However, disadvantages also exist in these gums, such as high cost (Paximada, Koutinas, Scholten, & Mandala, 2016), sophisticated extraction procedure (Pai, Srinivasarao, & Khan, 2002) and digesting and safety issue (Sharma et al., 2018). CNC as a natural emulsifying and stabilizing ingredient is of great interest in food products (Zanchetta, Rocchib, & Piazzab, 2017). Turbak, Kafrawy, Snyder, and Auerbach (1980) first proposed that nanocellulose could be used for water/oil emulsion. Since then, nanocellulose has been used as a natural emulsifier and stabilizer. In the cases studied, cellulose compared to the products which it replaces, like fat base cream fillings, brings similar organoleptic properties such as consistency and unctuousness (Shapira-Zaltsberg et al., 2018). CNC also replaces stabilizers and emulsifiers like hydrophilic polysaccharides extracted from seaweed, vegetable seeds, microorganisms or the like (Schacht, Bulcke, Delaey, & Draye, 2002). These bio-based particles from renewable resources are suitable options to develop Pickering emulsions. In this aspect, Visanko et al. (2014) extracted amphiphilic CNC from acid-free oxidative treatment and explored its application as oil-water stabilizer; Gong, Wang, and Chen (2017) modified woodbased CNC with phenyl trimethylammonium chloride, which was homogeneous/electrostatically stable in water and they can stabilize O/ W Pickering emulsions. Zhu, Ma, Li, Pan, and Dai (2015) applied CNC as stabilizer to synthesize multihollow magnetic imprinted microspheres by Pickering double water in oil in water emulsion polymerization. Ojala, Sirviö, and Liimatainen (2016) investigated the preparation and properties of marine diesel oil-in-water emulsion stabilized by bifunctionalized CNC.

4.2. Delivery systems Nutrients loss and active components inactivation have been huge challenge in food science and engineering (Alexander et al., 2017). First of all, nutrients and active components are easily reduced when subjected to high temperatures, low pH and mechanical forces during food processing (Truswell & Brand, 1985). Moreover, during transportation and storage, those food ingredients were deteriorated in unstable conditions (Mu et al., 2018). In addition, some nutrients (water soluble vitamins) and active ingredients (probiotics) can be destroyed by gastric juice and bile, which leads to a dramatic decrease in the amount that reaches the intestinal tract (Zhang, Zhang, Zhang, Decker, & McClements, 2015). An effective way to solve the problem is to build carriers called microcapsules and improve the delivery system (Ye, Georges, & Selomulya, 2018). Microcapsules are a conveyance system constructed with microparticles by using natural or synthetic polymers (Jones, Munford, & Gabbott, 1974). They have been shown to improve the bioavailability and biological activity of substances and decrease the side effects of functional food (Shutava & Lvov, 2012). Many biomolecules have been applied in microencapsulation of nutrients and active ingredients, such as sodium alginate (Németh et al., 2018), chitosan (Li et al., 2008), konjac glucomannan (Zhang, Chen, & Yang, 2014), and soy proteins (Gan, Cheng, & Easa, 2008). CNC is a food grade material with high biocompatibility and has been used in delivery system (Vashist et al., 2018). Hydrogels reinforced with CNC exhibited increasing orders-of-magnitude in the mechanical strength, high extension in degradation and the sustained release time (Yang, Bakaic, Hoare, & Cranston, 2013). For instance, 25% CNC can improve the storage modulus of the CNC-gelatin hydrogel from 122 Pa to 468 Pa (Ooi, Ahmad, & Amin, 2015). The chemically modified CNC can provide the sustained drug release ascribed to the “nano-obstruction effect” and “nanolocking effect” in delivery system (Lin, Geze, Wouessidjewe, Huang, & Dufresne, 2016). Huq et al. (2017) investigated the effect of CNC on alginate base nanocomposite for microencapsulation of probiotic. CNC improved the compression strength of the alginate hydrogel over 30%, and reduced the porosity of alginate matrix during freeze-drying. Furthermore, the swelling of the alginate microcapsules at pH 1.5 were decreased from 377% to 200% after CNC

4.4. Functional food ingredients The functional food industry, consisting of food, beverage and supplement sectors, is one of the several areas of the food industry that is experiencing fast growth in recent years (Helkar & Sahoo, 2016). Functional food is a food given an additional health-promotion or disease prevention function by adding new ingredients or more of existing ingredients (Childs, 2016). Various kinds of dietary fiber -enriched food products have been launched into the market to offer new choices for consumers (López-Marcos, Bailina, Viuda-Martos, Pérez-Alvarez, & Fernández-López, 2015). However, incorporated dietary fiber could adversely impact on the color, texture, flavor and taste in food products (Robin, Schuchmann, & Palzer, 2012). To make the best application as 139

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Fig. 3. Digestion and absorption of CNC in human body (Produced from Koshani & Madadlou, 2018).

pasting, and short- and long-term retrogradation properties of normal maize starch (NMS), waxy maize starch (WMS), and sweet potato starch (SPS). It is proved that the addition of CNC could inhibit the starch retrogradation, and the effect was dependent on the addition dosage of CNC (Cui et al., 2017). The mechanism of retrogradation inhibiting from CNC is mainly due to the association between starch and CNC, especially when crosslinking agent introduced, like (NaPO3)6 (Liu, Yang, Zhang, & Gao, 2017). In particular, it is approved that CNC with large specific surface area and lots of hydroxyl groups could interact with amylose by hydrogen bonding, to inhibit short-term retrogradation. On the other hand, the inhibition of long-term retrogradation could be attributed to the interplay between CNC and the amylopectin (Cui et al., 2017). In addition of inhibiting starch retrogradation, CNC is also a good candidate to construct cross linkage with molecular chains of starch (Nasution, Afandy, & Alfath, 2017). Liu et al. (2017) investigated the effect of CNC on the cross-linking reaction with oxidized potato starch. In this study, the result showed the cross-linking reaction occurred mainly in the non-crystalline region of the potato starch and only partly in the crystalline region due to degree of crystallinity decreasing. Finally, an enhanced starch material was produced for application in materials science. Although the aim of this study was to produce excellent materials from starch, the mechanisms can also be applied to explain some phenomenon in food science. Based on these findings, Ji, Liu, Li, Sun, and Xiong (2018) investigated the interaction of CNC and amylase, which influenced on enzyme activity and resistant starch (RS) content. The result reveled that in gelatinized starch, the addition of CNC induced a decrease in rapidly digestible starch (RDS) and slowly digestible starch (SDS) contents, but an increase in resistant starch (RS) contents. There are increases of 30.41%, 23.13%, and 20.30% in RS contents for corn, pea, and potato starches, respectively. RS, also known as enzyme resistant starch and difficult to digest starch, cannot be

functional food ingredient, nanocellulose was further extracted from natural sources to play a key role as a food additive (Gómez et al., 2016). The most used CNC as a functional food ingredient is its natural property as a dietary fiber. The advantage of the CNC can not only increase the content of the dietary fiber in food, but also overcome the negative effects from the traditional dietary fibers. Recently, obesity has become an important issue of concern. Much more attention is paid to low calorie/energy foods (Siep et al., 2009). Various ingredients like sugar alcohol (Allan, Rajwa, & Mauer, 2018), oligosaccharide (Unno, Yamamoto, & Nakakuki, 2008), bacterial fermentations (Patra, Tomar, & Arora, 2009) have been applied to produce functional food for weight control. The potential of nanocellulose to prepare reduced-fat formulations was also identified by Turbak and coworkers. Their patent (US 4378381) demonstrated that nanocellulose may be substituted for oil to produce a low-calorie salad dressing. Robson (2011) suggested self-assembled nanocellulose may be used to lower the energy density of many processed foods to < 1.6 kcal g−1. In addition, CNC was also applied as a new nanoscale product in foods such as ice cream, salad dressing, milk products and bread instead of high heat energy materials such as fat (Dunn & Finocchiaro, 1997).

4.5. Applications in starch foods CNC is not only an ingredient to exhibit functions in food products, but also can improve the quality of specific contents of food. In food industry, starch is applied as a thickening, gelling, bulking, or stabilizing agent. However, sophisticated food processing always affects the stability of food ingredients (Lu, Luo, & Xiao, 2012). The transformations that occur in the cooling and storage of gelatinized starch are referred as “retrogradation”, which usually deteriorates the quality of starchy food (Chen, Ren, Zhang, Tong, & Rashed, 2015). In this situation, Cui et al. (2017) evaluate the effect of CNC on the gelatinization, 140

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by EU around nanotoxicity have started in recent years. The project “GUIDEnano” was to develop innovative methodologies to evaluate and manage human and environmental health risks of nano-enabled products, including nanocellulose (Lynch, 2017). In 2018, The European Food Safety Authority (EFSA) has published its guidance on how to assess the safety of nanoscience and nanotechnology applications (Hardy et al., 2018). This guidance proposed approaches to risk characterization and uncertainty analysis, and hopefully can provide recommendations for further research in CNC.

enzymatically hydrolyzed in the small intestine, but it can be fermented with volatile fatty acids in the human intestinal tract colon. Therefore, CNC is not only a dietary fiber can be applied in low energy food, but also to make a healthier starchy food with “weight losing” functions. 5. Safety issue of CNC Productions of CNC present excellent properties, which make them potential applications in food industry. However, CNC is a nano scale derivative still exhibits unknown properties and thus may expose humans and the environment to unknown risks (Endes et al., 2013). CNC is exposed to a wide range of conditions when they are ingested. Fig. 3 illustrates a brief schematic for the digestion and absorption of CNC. Health and safety aspects of CNC have been recently evaluated (Dong, Hirani, Colacino, Lee, & Roman, 2012), the inhalation of plentiful CNC may induce pulmonary inflammation due to the easy selfaggregation and nondegradation of nanocellulose in the body of animals. In this aspect, Kovacs et al. (2010) initially studied the inherent eco-toxicology of cellulose nanocrystals with aquatic organisms. Clift et al. (2011) investigated toxicity of aerosolized CNC on the human airway with a co-culture of human monocyte-derived macrophages, dendritic cells and a bronchial epithelial cell line; Ni et al. (2012) reviewed the cytotoxicity evaluation with L929 cells of the cellulose nanowhiskers. Dong et al. (2012) discussed the cytotoxicity evaluation with 9 different cell lines of CNC. All above studies got similar conclusion that the novel CNC exhibited low cytotoxicity potential. Orogastrointestinal processing of CNC was also investigated to explore the behavior of CNC in human digesting system. Due to being indigestible entities, CNC is expected to trip through the gastrointestinal tract and end into stool. However, alimentary canal bioelectrolytes may influence the solubility and colloidal state of CNC particles which may in turn impact the interaction of CNC with intestinal lumen components (Koshani & Madadlou, 2018). A number of organizations have announced CNF and CNC demonstration plants in Europe and North America. The United States Food and Drug Administration (FDA) has issued several guidance documents on topics relating to the application of nanotechnology in FDA-regulated products. Bacterial and powdered cellulose have their application regulated and is “Generally Recognized As being Safe” (GRAS) by FDA, based on their long history of usage in foodstuffs (FDA, 2006; FDA, 2012). Numerous companies active in making Nanocellulose, like Fiberlean Technologies (US), Celluforce (Canada), etc. Fiberlean MFC has received clearance from the Food and Drug Administration (FDA) for use as a food contact substance in paper and paperboard for food packaging applications. A Food Contact Substance (FCS) Notification became effective on July 3, 2018. This FCN allows up to 5 wt percent of FiberLean MFC fibrils in the packaging (FDA, 2018). Celluforce also claimed their CNC products received regulatory clearances in multiple jurisdictions, include Canada's Domestic substances list (DSL) and Toxic Substances Control Act (TSCA) regulations in the US (Berry, 2019). Compare to North America, European countries are more interested in CNF, for instance reported organizations of Centre Technique du Papier (France), Stora Enso (Finland), UPM Fibril cellulose (Finland), Borregaard Chemcell (Noway), etc. (Lin & Dufresne, 2014). One survey showed that there only exist a few published peer reviewed articles into the toxicological effects of nanocellulose (CNF and CNC). Many of the studies performed has also been short term (Hanif, Ahmed, Shin, Kim, & Um, 2014; Kovacs et al., 2010; Menas et al., 2017; Pitkänen et al., 2010; Vartianinen et al., 2011), and more investigations on low exposure during long time are needed. In one case (Menas et al., 2017), CNF presented more toxic than CNC with respect to cytotoxicity and oxidative stress responses. This may contributes to the long fibril structure of the CNF. The fibers is too long for the macrophage cell to completely devour it, hence lead to a potential carcinogenic effect or fibrosis (Endes et al., 2016). Up to date, there is still no common regulation for nanocellulose, especially for CNC in the EU. Several projects financed

6. Conclusion and future perspectives CNC has been known for more than 50 years, and their infinite potential and application values were discovered increasingly. Their unique nanostructures give excellent physical and chemical properties of CNC to play vital roles in food industry. Meanwhile, CNC can be used as a low calorie replacement for carbohydrate additives used as thickeners, flavor carriers and suspension stabilizers in a wide variety of food products. The food applications were early recognized as a highly interesting application field for nanocellulose due to the rheological behavior of the nanocellulose gel. All previous works showed excellent functions of CNC in application of delivery system, which make it an ideal candidate to protect nutrients and active ingredients in food products. CNC can also be used in hydrogels to isolate the unexpected components present in human digesting system. It is obvious that the application of CNC has been deeply explored in food industry. However, several challenges still need to be overcome: 1) Microorganisms and marine products are recently emergent sources to produce biodegradable materials. Those sources could be used to further improve the yield, the quality and lower the price CNC. 2) To investigate the fermentation of CNC in human digestion. In the distal ileum and colon, CNC may interact with gut microbiome and influence their metabolism. It is however uncertain whether CNC-microbe interactions occur and whether they are detrimental, positive, or inconsequential. 3) Dietary fibers are good to reduce various diseases, such as diabetes, obesity, and cardiovascular disease. CNC is a type of dietary fiber that plays a beneficial role in the overall health of adults. To further explore the health benefit of CNC as dietary fiber will be another hot topic in future studies. 4) There are still no common regulations for CNC in worldwide, and detailed humans and the environment risks of CNC is need to be further explored. Researchers need further focused on their technological and nutritional properties evaluation, safety tests and most importantly, the question about the regulation for food application. References Abdallah, W., & Kamal, M. R. (2018). Influence of process variables on physical characteristics of spray freeze dried cellulose nanocrystals. Cellulose, 1–20. https://doi. org/10.1007/s10570-018-1975-0. Alexander, P., Brown, C., Arnethc, A., Finnigan, J., Moran, D., & Rounsevell, M. D. A. (2017). Losses, inefficiencies and waste in the global food system. Agricultural Systems, 153, 190–200. https://doi.org/10.1016/j.agsy.2017.01.014. Allan, M. C., Rajwa, B., & Mauer, L. J. (2018). Effects of sugars and sugar alcohols on the gelatinization temperature of wheat starch. Food Hydrocolloids, 84, 593–607. https:// doi.org/10.1016/j.foodhyd.2018.06.035. Arias, A., Heuzey, M. C., Huneault, M. A., Ausias, G., & Bendahou, A. (2015). Enhanced dispersion of cellulose nanocrystals in melt-processed polylactide-based nanocomposites. Cellulose, 22(1), 483–498. https://doi.org/10.1007/s10570-014-0476-z. Bahramparvar, M., Mazaheri Tehrani, M., & Razavi, S. M. A. (2013). Effects of a novel stabilizer blend and presence of κ-carrageenan on some properties of vanilla ice cream during storage. Food Bioscience, 3, 10–18. https://doi.org/10.1016/j.fbio. 2013.05.001. Berry, R. (2019). Improving barrier properties with cellulose nanocrystals. Chicago: Global Pouch Forum June, 2019. Boonterm, M., Sunyadeth, S., Dedpakdee, S., Athichalinthorn, P., Patcharaphun, S., Mungkung, R., et al. (2015). Characterization and comparison of cellulose fiber extraction from rice straw by chemical treatment and thermal stem explosion. Journal of Cleaner Production, 134, 592–599. https://doi.org/10.1016/j.jclepro.2015.09.084. Borkotoky, S. S., Dhar, P., & Katiyar, V. (2018). Biodegradable poly (lactic acid)/cellulose nanocrystals (CNCs) composite microcellular foam: Effect of nanofillers on foam

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