Escalating the technical bounds for the production of cellulose-aided peach leathers: From the benchtop to the pilot plant

This contribution falls within the context of sustainable functional materials. We report on the production of fruit leathers based chiefly on peach pulp, but combined with hydroxypropyl methylcellulose (HPMC) as binding agent and cellulose micro/nanofibrils (CMNF) as fillers.

Contents lists available atScienceDirect Carbohydrate Polymers journal homepage:www.elsevier.com/locate/carbpol

Escalating the technical bounds for the production of cellulose-aided peach

leathers: From the benchtop to the pilot plant

Giuliana T Francoa,b,1, Caio G Otonia,c,1,* , Beatriz D Lodia, Marcos V Lorevicea,

Márcia R de Mourad, Luiz H.C Mattosoa,*

aNanotechnology National Laboratory for Agriculture (LNNA), Embrapa Instrumentation, Rua XV de Novembro, 1452, São Carlos, SP 13560-979, Brazil

bPPGQ, Department of Chemistry, Federal University of São Carlos, Rod Washington Luís, km 235, São Carlos, SP 13565-905, Brazil

cDepartment of Materials Engineering, Federal University of São Carlos, Rod Washington Luís, km 235, São Carlos, SP 13565-905, Brazil

dDepartment of Physics and Chemistry, FEIS, São Paulo State University, Av Brasil, 56, Ilha Solteira, SP 15385-000, Brazil

A R T I C L E I N F O

Keywords:

Prunus persica

Continuous casting

Edible film

Ternary mixture design

Response surface methodology

Food packaging

A B S T R A C T This contribution falls within the context of sustainable functional materials We report on the production of fruit leathers based chiefly on peach pulp, but combined with hydroxypropyl methylcellulose (HPMC) as binding agent and cellulose micro/nanofibrils (CMNF) as fillers Increased permeability to moisture (from 0.9 to 5.6 g

mm kPa−1h−1m−2) and extensibility (from 10 to 17%) but reduced mechanical resistance (67–2 MPa) and stiffness (1.8 GPa–18 MPa) evidenced the plasticizing effect of peach pulp in HPMC matrix, which was reinforced

by CMNF A ternary mixture design allowed building response surfaces and optimizing leather composition The

laboratory-scale leather production via bench casting was extended to a pilot-scale through continuous casting.

The effect of scaling up on the nutritional and sensory features of the peach leather was also depicted The herein established composition-processing-property correlations are useful to support the large-scale production of peach leather towards applications both as packaging materials and as nutritional leathers

1 Introduction

Strategies towards increased shelf life have become increasingly

demanded due to the complex food supply chain faced by today’s

so-ciety, involving long distances and periods of transportation and

sto-rage Packaging systems have gained prominence due to their role as

physical hurdles against food dehydration and spoilage Ongoing is also

the trend of replacing petrochemical building blocks of

non-biode-gradable materials by rapidly renewable raw materials for

biodegrad-able packaging (Ahmadzadeh & Khaneghah, 2019) This drives one’s

attention not only to what comes from Nature, but also to what goes

back to the environment Edible packaging – i.e., that comprising

ex-clusively food-grade components, regardless of processing (Cerqueira,

2019) – stands out in this context, particularly for single-use

applica-tions, as waste is either not generated or readily biodegradable Should

such materials be also intended to protect foodstuffs, these must per-form suitably from the physical-mechanical standpoint, as extensively demonstrated for edible coating and self-standing films based on naturally occurring polysaccharides and polypeptides (Atarés & Chiralt,

2016;Dehghani, Hosseini, & Regenstein, 2018)

Fruits and vegetables have been increasingly exploited as edible film-forming matrices, in combination with natural polymer or by themselves thanks to their typically high loads of carbohydrates and/or proteins (Otoni et al., 2017) Depending on the formulation and pro-cessing conditions, self-standing edible layers having fruit pulp or puree

as main ingredient can behave rheomechanically like thermoplastics – bioplastics – or present a leathery consistency – fruit leathers (Otoni

et al., 2017) Both approaches may not only contribute to solving the aforementioned sustainability related issues, but also to human health because of their nutritional load, as well as to consumer perception due

https://doi.org/10.1016/j.carbpol.2020.116437

Received 5 February 2020; Received in revised form 9 April 2020; Accepted 9 May 2020

Abbreviations: ANOVA, analysis of variance; CMNF, cellulose micro/nanofibrils; DPPH, 2,2-diphenyl-1-picrylhydrazyl; HPMC, hydroxypropyl methylcellulose; LFF,

leather-forming formulations; MW, molecular weight; RDI, recommended daily intakes; RH, relative humidity; Trolox, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid; WVP, water vapor permeability

⁎Corresponding authors at: Nanotechnology National Laboratory for Agriculture (LNNA), Embrapa Instrumentation, Rua XV de Novembro, 1452, São Carlos, SP 13560-970, Brazil

E-mail addresses:gtfranco@estudante.ufscar.br(G.T Franco),otoni@unicamp.br(C.G Otoni),beatrizdlodi@hotmail.com(B.D Lodi),

marcos.lorevice@lnnano.cnpem.br(M.V Lorevice),marcia.aouada@unesp.br(M.R.d Moura),luiz.mattoso@embrapa.br(L.H.C Mattoso)

1These authors contributed equally

Available online 24 May 2020

0144-8617/ © 2020 Elsevier Ltd All rights reserved

T

to their unique sensory features The possibilities of using overripe

produce (Aguirre-Joya et al., 2018) or even side streams from its

pro-cessing (Otoni, Lodi et al., 2018) make such a novel class of materials

further appealing by valorizing typically underutilized resources, which

in turn is expected to culminate in diminished food waste It is

note-worthy that, owing to their low water activity levels, fruit leathers may

be taken as dehydrated foods and ought to be stable as far as microbial

spoilage as long as they are protected from moisture (Otoni et al.,

2017) From the shelf life standpoint, while fruit leathers are ideal to

wrap dry foodstuffs within also dry environments, these can be suitably

used in humid atmospheres provided they are further enclosed within a

high-barrier secondary packaging, but they are less likely to serve as

primary packaging for moist foods

In line, the exploitation of underutilized resources is also expected

to reduce production costs and to add value to otherwise discarded raw

materials Also related with the production costs of bioplastics and fruit

leathers is the material-forming method itself, which is traditionally

carried out in batch-mode solvent casting, process that involves

la-boratory scale, long drying times, and low yields – herein referred to as

bench casting (de Moraes, Scheibe, Sereno, & Laurindo, 2013;Otoni

et al., 2017) The continuous analogue of bench casting has been

de-monstrated to remarkably increase the yield of edible layers made up of

fruits and vegetables (Munhoz et al., 2018; Otoni, Lodi et al., 2018),

even though maintaining the properties remains challenging because of

the relatively low thermal stability of some of their constituents From

the mechanical standpoint, specifically, should fruit-only bioplastics

perform poorly, these can be combined to other food-grade matrices

and fillers, such as lignocellulosics – e.g., hydroxypropyl

methylcellu-lose (HPMC), a nonionic cellumethylcellu-lose ether that is widely known for its

film-forming ability (Hay et al., 2018) and for being generally

re-cognized as safe (FDA; GRAS Notice No GRN 000213, 2007) and

ap-proved as a food additive (US FDA, 21 CFR 172.874, 2011; and

Eur-opean Union, EPCD No 95/2/EC, 1995) Among these biorenewables,

cellulose micro/nanofibrils (CMNF) denote efficient fillers for

me-chanically reinforcing edible bioplastics (Valencia, Nomena, Mathew, &

Velikov, 2019;Viana, Sá, Barros, Borges, & Azeredo, 2018)

In the context presented above, this contribution is devoted to fruit

leathers comprising peach pulp as main component and HPMC and

CMNF, herein exploited as binding and reinforcing agents, respectively

The role played by each of these components on the

physical-me-chanical properties of the resulting materials was fully depicted

Finally, this study also set out to scale up the production of the peach

leathers from bench casting to its continuous equivalent, as well as to

either confirm or refute the hypothesis that the leather-forming

pro-tocol influences the key properties of such materials, including

nutri-tional and sensory aspects

2 Materials and methods

2.1 Materials

Pasteurized peach pulp (De Marchi, Brazil), HPMC Methocel® E4M

(CAS no 9004-65-3; The Dow Chemical Company, Brazil) –

compre-hensively characterized elsewhere [degree of substitution: 1.9; M w : ca.

350,000 g mol−1(Otoni, Lorevice, Moura, & Mattoso, 2018)] – and

2,2-diphenyl-1-picrylhydrazyl (DPPH) and

6-hydroxy-2,5,7,8-tetra-methylchroman-2-carboxylic acid, or Trolox (Sigma-Aldrich Co LLC,

USA) were used as received Microcrystalline cellulose Sigmacell® Type

50 (CAS no 9004-34-6; Sigma-Aldrich Brasil Ltd, Brazil) – ζ potential:

-1.0 ± 0.4 mV; apparent particle size: 1.6 ± 0.9 μm; crystallinity index:

62 ± 2% (Otoni, Carvalho et al., 2018) – was dispersed in water at 1%

(w/v) without any pretreatment or purification and high-pressure

mi-crofluidized (Microfluidizer® M-110 P; Microfluidics Corp., USA) for

seven cycles at 138 MPa into CMNF – ζ potential: -30 to -24 mV;

ap-parent particle size: 160−250 nm; crystallinity index: 70–75% (Otoni,

Carvalho et al., 2018) Ultrapure water (Barnstead Nanopure Diamond,

USA) was used in all experiments

2.2 Leather production via bench casting

The components listed above were mechanically stirred at 1500 rpm for 30 min under vacuum (500 mmHg) into leather-forming formula-tions (LFF) that were allowed to rest under vacuum for another 30 min

to remove bubbles before being spread with uniform thickness onto a poly(ethylene terephthalate) sheet, where they were dried at room temperature and 50 ± 10% relative humidity (RH) for 24 h Dried leathers were peeled from the casting surface and equilibrated at room temperature and 50% RH for at least 48 h in a desiccator containing saturated magnesium nitrate solution before used for testing

2.3 Leather production via continuous casting

Leathers were also produced in a continuous fashion on a KTF-B lamination system (Werner Mathis AG, Switzerland) that comprised

four main steps, namely: 1, feeding: the LFF was poured on a Mylar (DuPont Teijin Films U.S Ltd., USA) conveyor belt; 2, lamination: the

LFF was forced through a gap between the polyester substrate and a

knife into a 1.50-mm-thick, 26-cm-wide wet layer; 3, drying: the wet LFF layer was conveyed through an infrared pre-drying stage (at ca 45

°C and 0.10 m⋅min−1for 30 cm) and two convective drying stages (at

120 °C and 0.10 m min−1for 92 cm each); and 4, winding The

feeding-to-winding distance and time were 3 m and 30 min, respectively Prior

to any testing, dried leathers were stored as described previously

2.4 Experimental design, optimizations, and scale up

Peach pulp, HPMC, and CMNF were combined at different propor-tions according to a ternary mixture design (Table S1) The weight ratio (dry basis) of each component ranged from 0 to 1, their weighted contributions together adding up to 1 Bench casting (Section2.2) was used at this stage Tensile strength (T ), Young’s modulus (E), and

elongation at break (B) were determined by tensile assay on a DMA Q800 dynamic-mechanical analyzer (TA Instruments, Inc., USA), cal-culated by Eq.1to Eq.3, and taken as dependent variables for opti-mization purposes

= F A/

= L[( L)/ ]·100L

=

E lim /L

WhereF is the maximum load, L is the extension (at a given point:

no index; at the beginning of the assay: index 0; at break: index B), σ is

the stress at a given point, andA0is the initial cross-sectional area, the latter considering sample thickness, which was measured with a digital micrometer (Mitutoyo Corp., Japan) by averaging five random mea-surements The load cell was 18 N and the stretching rate was 0.1% min−1 The response variables were used to build response surfaces

To investigate the isolated effect of peach pulp on the mechanical and barrier properties of the leathers, 2.5, 5.0, or 7.5% (w/v) of peach pulp was mixed with 2% (w/v) of HPMC in water The LFF were con-verted into leathers by bench casting (Section2.2) and characterized as described in Sections2.5and2.6 Finally, to assess the effect of scaling

up leather production on its key properties, the optimum LFF (X PP=

0.85, X HPMC = 0.15; further discussion below) was also processed through continuous casting (Section2.3), and the nutritional and sen-sory properties of the continuously and bench-cast leathers were com-pared

2.5 Mechanical properties

The leathers were submitted to uniaxial tensile assay on a DL3000

universal testing machine (EMIC Equipamentos e Sistemas de Ensaio

Ltda., Brazil) equipped with a 10-kgf load cell At least six leather

specimens per treatment, shaped in accordance with ASTM D882−18,

were stretched at 10 mm min−1from an initial length (L0) of 100 mm

until rupture The mechanical attributes T, B , and E were calculated

using Eq.(1), Eq.(2), and Eq.(3), respectively

2.6 Barrier to water vapor

The water vapor permeability (WVP) of the leathers was measured

in accordance with the modification of ASTM E96−80 proposed by

McHugh, Avena-Bustillos, and Krochta (1993) In brief, at least four

leather specimens per treatment were fixed onto the edges of poly

(methyl methacrylate) capsules with circular openings of 5.1 cm in

diameter, serving as semi-permeable barriers between an inner high-RH

environment and a chamber at 30 ± 1 °C and 30 ± 2% RH The

cap-sules were weighed periodically to determine WVP

2.7 Antioxidant capacity

Continuously and bench-cast leathers (1−2 g, measured accurately)

were dipped in 20 mL 99.8% pure methanol at 4 °C for 24 h The

methanolic extracts were centrifuged (Rotina 380 R, Andreas Hettich

GmbH & Co KG, Germany) for 10 min at 15 °C and 10,000 rpm and had

their antioxidant capacities determined as described by

Brand-Williams, Cuvelier, and Berset (1995) Briefly, 0.1 mL of different di-lutions (in methanol) of the supernatant was mixed with 3.9 mL of a 0.0024% (w/v) solution of DPPH, also in methanol The mixtures were kept in the dark at room temperature for 30 min before having their absorbances at 515 nm measured on a UV-1601PC spectrophotometer (Shimadzu Co., Japan) Leather-free methanol and DPPH solutions were used as blank and control, respectively An analytical curve was ad-justed by varying the concentrations of Trolox – a standard antioxidant analogous to vitamin E – from 80 to 800 mg L−1and used to quanti-tatively express the antioxidant capacity of the leathers, in μg of Trolox equivalent per g of sample (μg g−1)

2.8 Content of minerals

The content of minerals in the fruit leathers was determined by atomic absorption spectrometry Continuously and bench-cast leathers (1−2 g, measured accurately) were digested in a mixture of nitric acid P.A (10 mL), hydrochloric acid P.A (5 mL), and 30 vol hydrogen peroxide (3 mL) on a Kjeldahl digester (model SL-25/40, Solab Equipamentos para Laboratório Ltda., Brazil) at 140 °C for 24 h and then filtered through filter paper into 50-mL volumetric flasks that were further completed with ultrapure water The resulting solutions were analyzed on a PinAAcle 900 T spectrometer (PerkinElmer, Inc., USA), with flame and radiation sources at specific wavelengths to determine the following minerals: Fe, 248.33 nm; K, 766.49 nm; Mg, 285.21 nm;

Fig 1 Surface response plots for the mechanical properties of biocomposites comprising different weight ratios of peach pulp (PP), hydroxypropyl methylcellulose

(HPMC), and cellulose micro/nanofibrils (CMNF)

Ca, 422.67 nm; Mn, 279.48 nm; and Na, 589.00 nm Analytical curves

were previously built with standard solutions of each of these minerals

and used for the quantitative interpretation of the results The runs

were carried out in triplicates

2.9 Colorimetric parameters

The color of the fruit leathers was determined on a CR-400 digital

colorimeter (Konica Minolta Sensing, Inc., Japan) The brightness (L*)

and the chromaticity parameters a* (red-to-green) and b*

(yellow-to-blue) were determined in at least three random positions along the

leather surfaces The LFF served as reference for calculating the total

color difference (ΔE) by Eq.4, wherein the subscript indexes L and LFF

refer to leather and leather-forming formulations, respectively

Yel-lowness index (YI) and whiteness index (WI) were calculated through

Eq 5 and Eq 6, respectively

E [(L L* L LFF* )2 (a L* a LFF* )2 (b L* b LFF* ) ]2 0.5 (4)

=

WI 100 [(100 L L* 2) a L*2 b L*2 0.5] (6)

2.10 Statistical treatment of data

Quantitative data were submitted to analysis of variance (ANOVA)

at 5% of significance followed by regression analysis or Tukey test at

the same level of significance, as suitable Mechanical data were fitted

to quadratic regression models according to the mixture design The

importance of model components was examined by ANOVA (also at

5%), and nonsignificant effects were disregarded from the models that

were used to plot response surfaces

3 Results and discussion

3.1 On the optimization of leather formulation

Physical-mechanical cohesion and integrity were herein taken as the

primary technical requirements for fruit leathers to be suitably used as

self-standing layers, application that would be prevented otherwise

This was the rationale for relying the optimization procedures upon the

tensile behavior of the peach leathers The surface response plots re-sulting from the ternary mixture design are presented inFig 1 The statistical procedure allowed establishing models that were efficient in fitting the acquired mechanical data The regression coefficients of such models are presented in Table S2

The response surface plots elucidate the role played by each of the components: HPMC serves as binding agent and leather-forming matrix, higher HPMC contents being accompanied by also higher tensile strengths; CMNF act as fillers for mechanical reinforcement, thus leading to stronger leathers; and peach pulp, introduced as the major functional ingredient, but from the mechanical standpoint behaving as

a plasticizer by increasing leather extensibility and decreasing its re-sistance and stiffness This mapping strategy allows one to engineer the mechanical properties of materials made up of such a system without the need for further testing Importantly, we demonstrate the possibility

of producing biocomposite leathers with varying mechanical perfor-mances by simply altering the composition of the LFF, ranging from rubbery self-standing layers – suitable for applications as edible

lea-thers, for instance – all the way to stiff sheets – suitable for e.g food

packaging Because we targeted at leather that are functional – and as preliminary tests showed that neither HPMC nor CMNF themselves have antioxidant activity – but still provide sufficient mechanical strength to be used as self-supporting layers, the LFF chosen for the further steps comprised 85 wt.% peach pulp and 15 wt.% HPMC This approach is illustrated inFig 2 It is worth stressing out that, should superior mechanical properties be required for a given application, the established relationships can be used to alter the LFF and produce materials with tailored mechanical performance

3.2 On the role of peach pulp on HPMC matrix

Because peach pulp and HPMC were selected as the constituents of the peach leathers, the effect of mixing them at different proportions was further investigated as far as mechanical and water barrier prop-erties (Fig 3)

All of the evaluated properties were affected (P < 0.05) by com-position Peach pulp itself formed a continuous layer that was easily detachable from the casting surface, although with extremely low stiffness and resistance while with high extensibility As expected, higher peach pulp contents led to leathers featuring lower resistance and stiffness, but higher extensibility and permeability to moisture This

Fig 2 Left: formulations of peach leathers using hydroxypropyl methylcellulose (HPMC) as binder and of biocomposites comprising cellulose micro/nanofibrils

(CMNF) as fillers; right: leather-forming formulation before (top) and after (bottom) drying either on lab- (bench casting) or pilot-scale (continuous casting) The insets show dried leather specimens shaped for tensile assays

effect, which is typical of plasticizers, had already been reported after

the incorporation other fruit pulps and purees (e.g., guava and papaya)

into HPMC films (Lorevice, Moura, de, Aouada, & Mattoso, 2012;

Lorevice, Moura, de, & Mattoso, 2014) This effect can be attributed to

low-molecular weight (M W) compounds that are naturally found in

fruits, such as mono, di, and oligosaccharides (Espitia et al., 2014) As a

matter of fact, 100 g fresh peach has been shown to contain 5.2–8.8 g

sucrose – M W: 342.3 g⋅mol−1– ca 1.2 g of glucose – M W: 180.2 g mol−1

– and 1.1–1.4 g of fructose – M W: 180.2 g⋅mol−1(Cascales, Costell, &

Romojaro, 2005) These low-M Wcomponents can easily accommodate

themselves between HPMC chains – M W ca 330,000 g mol−1for the

E4M grade –, separating them apart In the context of mechanical

performance during uniaxial tensile assay, this plasticizing behavior

lessens the level of intermolecular interaction and allows adjacent

HPMC chains to flow more freely one over another Regarding barrier

to moisture, separating HPMC chains increases the intermolecular

vo-lume and reduces the tortuosity of the path followed by the permeant,

in this case water vapor Water molecules can therefore diffuse more

easily from the high- to the low-RH environments, culminating in

higher WVP values

3.3 On the effect of scaling up leather production

Peach leathers were successfully produced through both bench and

continuous casting procedures (Fig 2) The pilot-scale approach of

drying the LFF indeed boosted water removal: whereas the dried leather was detached from the bench casting substrate 24 h after the deposition

of the LFF, the feeding-to-winding time in the continuous casting was

only 30 min, i.e., a significant 48-time reduction This was allowed by

the infrared pre-drying stage and the convective drying at higher temperatures As reported byOtoni, Lodi et al (2018), who produced carrot-based biocomposites using the same apparatus and conditions,

this aspect is important because ca 75 m2would be needed to produce such an area of leather through bench casting, number that would be

reduced to ca 5 m2for continuous casting This discrepancy gets in-creasingly enlarged as the production volume increases, corroborating the relevance of scaling up the production of fruit leathers in the di-rection of large-scale industrial operations

As important as the yield is the maintenance of the key features of fruit leathers, which are to be preserved even after harsher processing conditions In this context, the antioxidant capacity, color, and content

of minerals were compared in the continuously and bench-cast leathers The antioxidant capacity of both leathers as well as their contents of the minerals K, Na, Mg, Ca, Fe, and Mn are presented inTable 1 The processing method had either low or no influence on the mi-neral content, which was somehow expected due to the high thermal stability of these compounds Considering the recommended daily in-takes (RDI) of these minerals in adult diets, as defined by the Brazilian Health Regulatory Agency (ANVISA) through Resolution RDC No 269, the produced leathers, regardless of the processing method, can be classified as sources – 100 g of leather provide more than 15% of the RDI – of the macronutrient potassium and the micronutrient manga-nese Additionally, these leathers are classified as having high contents – 100 g of leather provides more than 30% of the RDI – of the micro-nutrient iron Also importantly, it is classified as having low sodium content – 100 g of leather comprises less than 120 mg of sodium

As for the antioxidant capacity, the processing at higher tempera-tures led to a reduction, but both continuously and bench-cast leathers were highly antioxidant This is also expected as fruits and vegetables are overall known to have several antioxidant compounds, including phenolics, flavonoids, terpenes, sterols, saponins, glycosinolates, and carotenoids, being often associated with reduced risk of cardiovascular disease, cancer, arteriosclerosis, and other diseases related to the aging process and induced by the formation of free radicals (Du, Avena-Bustillos, Breksa, & McHugh, 2014) Through different mechanisms,

Fig 3 Mechanical properties and water vapor permeability (WVP) of peach leathers made up of the combination, at different weight ratios (dry basis) of peach pulp

and hydroxypropyl methylcellulose Dotted lines indicate fittings to actual data points, whose equations are presented as Supplementary Material (Eq S1 to Eq S4)

Table 1

Antioxidant capacity (AC), contents of minerals, and their recommended daily

intakes (RDI) in peach leathers produced on laboratory and pilot scales

Mineral Bench casting

/mg 100 g −1 Continuous casting

/mg 100 g −1 RDI

/mg 100 g −1

AC (μg Trolox g−1 ) 2920 ± 21 b 2555 ± 58 a –

abWithin a row, different mean ± standard deviation values (P < 0.05) are

followed by different superscript letters

these compounds are able to stop oxidative reactions in their early

stages by the accepting free radicals, donating hydrogen atoms to serve

as free radical acceptors, or chelating metals that catalyze oxidative

reactions (Eça, Machado, Hubinger, & Menegalli, 2015; Reis et al.,

2015) In peach, specifically, high levels of carotenoids, flavonoids,

anthocyanins, and hydroxycinnamate have been reported (Gil,

Tomás-Barberán, Hess-Pierce, & Kader, 2002;Zhao et al., 2015) The RDI of

antioxidant compounds for benefiting human health is from 0.75 to

0.90 g of Trolox, and fruit and vegetable intake accounts for 0.3−0.4 g

Trolox d−1(Prior & Cao, 2000), corroborating the relevance of having

leathers as an extra form of fruit intake In addition to the benefits to

human health, the antioxidant capacity of bioplastics, and therefore of

fruit leathers, can also be advantageous in the case of food preservation,

since oxidation reactions of organic molecules represent one of the

main mechanisms of food spoilage: besides causing nutritional – by the

loss of vitamins and essential fatty acids – and sensory depreciation – by

the occurrence of oxidative rancidity –, toxic compounds can be

pro-duced (Reis et al., 2015)

Color was taken as an indicator of the sensory quality of the peach

leathers, as it is indeed one of the most important attributes affecting

food appearance and having a pronounced influence on consumers'

perception The colorimetric parameters of the leathers are presented in

Table 2

Simply drying the LFF into leathers, regardless of the method,

in-creased the values of the three coordinates of the CIELab scale, behavior

which can be attributed to the concentration of chromophore

com-pounds The similar total color difference values – which takes the three

colorimetric coordinates into account – between the continuously and

bench-cast leathers, in relation to the precursor LFF, suggest that the

overall color variation was not affected by the processing protocol

When the coordinates are analyzed as isolated variables, however, the

scaled up leathers were darker than those produced by bench casting, as

indicated by the higher L* values and whiteness index of bench cast

leathers This is attributed to non-enzymatic browning reactions, like

the Maillard reaction, which involves the interaction between reducing

carbohydrates (mainly fructose and glucose in the case of peach) and

amino acids and/or proteins upon heating, culminating in the

produc-tion of dark-colored compounds such as melanoidins Peach darkening

kinetics has been shown to be temperature-dependent, being faster at

higher temperatures, as well as to involve carotenoid degradation

during heat treatment, leading to the depreciation of the yellowish

coloration and the enhancement of the reddish hue (Ávila & Silva,

1999) Indeed, the herein produced peach leathers attained a stronger

red color when processed at 120 °C – indicated by the higher a* value –

but yellowing did not follow the same trend It is important mentioning

that bench casting peach leather could also cause enzymatic browning

reactions, but the previous pasteurization of the peach pulp is expected

to inactivate the oxidative enzymes (e.g., peroxidase and

poly-phenoloxidase) responsible for such processes Finally, although high

mechanical and barrier performances were not targeted for the herein

produced peach leathers, it is noteworthy that the WVP of bench

(7.7 ± 0.9 g mm kPa−1h−1m−2) and continuously (6.8 ± 0.2 g mm kPa−1h−1m−2) cast leathers was not affected (P > 0.05) by the lea-ther-forming method The tensile resistance (3.5 ± 0.1 to 2.6 ± 0.1 MPa), stiffness (44 ± 1 to 36 ± 2 MPa), and extensibility (14.4 ± 0.3 to 12.6 ± 0.6%), conversely, were slightly reduced when the casting process was scaled up

4 Conclusions

The pilot-scale production of peach leathers was herein demon-strated to be feasible in terms of physical-mechanical, nutritional, and sensory properties The interdependency among leather composition, leather-forming parameters, and leather properties was also elucidated, confirming the roles played by peach pulp as the main component, HPMC as binding agent, and CMNF as filler In particular, peach pulp presented a typical plasticizing behavior, decreasing both resistance and stiffness while increasing extensibility and WVP of peach leathers CMNF, on the other hand, were efficient in providing mechanical inforcement The continuous casting approach was successful in re-moving the dispersant medium of the LFF in a significantly faster fashion, boosting yield and productivity while maintaining the key characteristics of the final materials, refuting the initial hypothesis The mineral content, for instance, was not impacted, while the continuously cast leathers presented an even more reddish aspect than their

bench-cast analogues, increasing the association of the former with in natura

peach Both leathers presented high antioxidant capacity, although slightly reduced in the leather processed at higher temperatures Altogether, our results help pave the route for the large-scale produc-tion of fruit-based materials towards industrial applicability both as packaging materials and as nutritional leathers

Funding

This work was supported by the São Paulo Research Foundation (FAPESP) [grant numbers 2013/14366-7, 2014/23098-9, and 2019/ 06170-1], National Council for Scientific and Technological Development (CNPq) [grant numbers 303796/2014-6, 312530/2018-8, and 800629/2016-7], Coordination for the Improvement of Higher Education Personnel (CAPES) [grant numbers 33001014005D‐6 and 88882.332747/2019-01], and Ministry of Science, Technology, and Innovation (MCTI/SISNANO) [grant number 402287/2013-4]

CRediT authorship contribution statement Giuliana T Franco: Writing - original draft, Investigation Caio G Otoni: Conceptualization, Investigation, Writing - original draft Beatriz D Lodi: Investigation Marcos V Lorevice: Investigation,

Writing original draft Márcia R de Moura: Supervision, Writing -review & editing Luiz H.C Mattoso: Conceptualization, Funding

ac-quisition, Project administration, Supervision, Writing - review & editing

Declaration of Competing Interest

None

Acknowledgements

The authors are thankful for the financial support of FAPESP (grants

no 2013/14366-7, no 2014/23098-9, and no 2019/06170-1), CNPq (grants no 303796/2014-6, no 312530/2018-8, and no 800629/ 2016-7), SISNANO/MCTI (grant no 402287/2013-4), CAPES (grants

no 33001014005D‐6 and 88882.332747/2019-01), FINEP, and Embrapa AgroNano research network The gracious donation of HPMC samples by The Dow Chemical Company is also acknowledged

Table 2

Colorimetric parameters of peach leather-forming formulations (LFF) and

lea-thers produced on laboratory (bench casting) and pilot (continuous casting)

scales

Parameter LFF Bench casting Continuous casting

abcWithin a row, different mean ± standard deviation values (P < 0.05) are

followed by different superscript letters

Appendix A Supplementary data

Supplementary material related to this article can be found, in the

online version, at doi:https://doi.org/10.1016/j.carbpol.2020.116437

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