Effects of edible chitosan- linseed mucilage coating on quality and ...

<strong>Effects</strong> <strong>of</strong> <strong>edible</strong> <strong>chitosan</strong>- <strong>linseed</strong> <strong>mucilage</strong> <strong>coating</strong> on quality and shelf life <strong>of</strong> freshcut
strawberry
Laura Eugenia Pérez Cabrera a , Gloria Cristina Díaz Narváez a , Alberto Tecante Coronel b , Chelo González
Martínez c
a Department <strong>of</strong> Food Technology, Universidad Autónoma de Aguascalientes, Aguascalientes, México
(leperez@correo.uaa.mx)
b Department <strong>of</strong> Food and Biotechnology, Universidad Nacional Autónoma de México, Ciudad de México
c Department <strong>of</strong> Food Technology, Universidad Politécnica de Valencia, Valencia, Spain
ABSTRACT
The increment on consumer demands <strong>of</strong> high quality foods and the concern <strong>of</strong> the environment deterioration
have forced to the food processors to reduce disposable packaging waste and have led to increase research
interest on <strong>edible</strong> films and <strong>coating</strong>s. Edible <strong>coating</strong>s provide an additional protective <strong>coating</strong> fruits and
vegetables minimally processed, which is equivalent to the technological impact <strong>of</strong> a modified atmosphere,
representing an alternative to conservation, coupled with an environment friendly method. The objective <strong>of</strong>
this study was evaluated the effectiveness <strong>of</strong> <strong>edible</strong> <strong>chitosan</strong>-<strong>linseed</strong> <strong>mucilage</strong> <strong>coating</strong>s to extend the shelflife
<strong>of</strong> strawberries minimally processed. Edible <strong>coating</strong>s made with flaxseed <strong>mucilage</strong>, <strong>chitosan</strong> 1%, lactic
acid 0.5% and Glycerol 0.6%. It dipped strawberries, washed and sanitized in the <strong>edible</strong> <strong>coating</strong>s and stored
at 10 ° C to facilitate dry, then were packed in polystyrene bags at 4 ° C. Uncoated strawberries were used as
a blank and covered strawberries without <strong>chitosan</strong> in the formulation and control. Were analyzed respiration
rate, colour, decay rate, texture, microbial growth and weight loss at 0 days and during storage (20 days). The
<strong>edible</strong> <strong>coating</strong> samples with <strong>chitosan</strong> in its formulation, have a significantly lower compared with control RR
to 0 days. The colour and firmness <strong>of</strong> the strawberries with <strong>edible</strong> <strong>coating</strong>s to the end <strong>of</strong> storage showed less
changes compared to day 0, weight loss was significantly higher for control samples and the decay rate
showed that <strong>edible</strong> <strong>coating</strong>s containing strawberries have less damage Chitosan expressed as tissue
desiccation, presence <strong>of</strong> fungi and collapse. Coating application with <strong>chitosan</strong> in its formulation reduces
significantly microbial growth in fresh-cut strawberry. From these observations, it appears that the
experimental <strong>coating</strong>s had a positive effect on maintaining quality. However, a longer testing period is
needed to re-enforce the findings from this study.
Keywords: <strong>linseed</strong> <strong>mucilage</strong>; <strong>chitosan</strong>; strawberry; shelf life; quality
INTRODUCTION
The use <strong>of</strong> <strong>edible</strong> <strong>coating</strong>s represents one <strong>of</strong> the important methods being used for preserving quality <strong>of</strong>
minimally processed produce; several mechanisms are involved in extending the shelf-life <strong>of</strong> fruits and
vegetables. Edible <strong>coating</strong>s have been traditionally used to improve food appearance and maintain quality
because they are considered environmentally friendly [1]. Coating films can act as barriers to moisture and
oxygen during processing, handling and storage [2]. Moreover, they can retard food deterioration by
inhibiting the growth <strong>of</strong> microorganisms, due to their natural intrinsic activity or to the incorporation <strong>of</strong>
antimicrobial compounds [3]. Normally, <strong>edible</strong> films are made <strong>of</strong> proteins or polysaccharides that can also
help to maintain moisture, thereby improving shelf life. However, the hydrophilic nature <strong>of</strong> these compounds
limits their ability to provide desired <strong>edible</strong> film functions. Current approaches to extend functional and
mechanical properties <strong>of</strong> these films include (i) incorporation <strong>of</strong> hydrophobic compounds such as lipids to
improve their resistance to water [4], (ii) optimization <strong>of</strong> the interaction between polymers (protein-protein
interactions, charge–charge electrostatic complexes between proteins or polysaccharides) and (iii) crosslinking
or functionalization through physical, chemical, or enzymatic treatments [5].
Strawberries are a non-climacteric fruits with a very short postharvest life. Strawberries are especially
perishable fruits, being susceptible to mechanical injury, desiccation, decay and physiological disorders
during storage [6]. Loss <strong>of</strong> quality in this fruit is mostly due to its relatively high metabolic activity and
sensitivity to fungal decay

Linseed <strong>mucilage</strong> is capable to film-forming [7]; the functionality <strong>of</strong> <strong>linseed</strong> <strong>mucilage</strong> is similar to that <strong>of</strong>
gum arabic [8]. Linseed <strong>mucilage</strong> and <strong>linseed</strong> <strong>mucilage</strong>-based <strong>edible</strong> <strong>coating</strong>s have been used in fresh-cut
cucumber resulting from better preservation did not induce significant changes in physicochemical quality
throughout cold storage, but they did result in a better preservation <strong>of</strong> the coated samples mechanical
properties and colour during storage. From these observations, it appears that the experimental <strong>coating</strong>s had a
positive effect on maintaining quality [6]. However <strong>linseed</strong> <strong>mucilage</strong>-based <strong>edible</strong> <strong>coating</strong>s does not present a
significant reduction in antimicrobial activity, that is why the combination with antimicrobial agents is
necessary, such as <strong>chitosan</strong>.
Chitosan (poly β-(1,4)N-acetyl-D-glucosamine) polymer is industrially produced by chemical deacetylation
<strong>of</strong> the chitin found in arthropod exoskeletons. This biopolymer can also be obtained directly from the cell
wall <strong>of</strong> some plant-pathogenic fungi. Chitosan and its derivatives have been shown to inhibit the growth <strong>of</strong> a
wide range <strong>of</strong> fungi and trigger defensive mechanisms in plants and fruits against infections caused by
several pathogens. Chitosan possesses excellent film-forming properties and can be applied as an <strong>edible</strong>
surface <strong>coating</strong> to fruits and vegetables. Chitosan <strong>coating</strong>s have been reported to limit fungal decay and delay
the ripening <strong>of</strong> several commodities, including strawberry [9]. In addition, <strong>chitosan</strong> is an ideal preservative
<strong>coating</strong> for fresh fruits because <strong>of</strong> its biochemical properties [9] and its use in food is particularly promising
because <strong>of</strong> its ‘‘biocompatibility’’, non-toxicity and antimicrobial action. The objective <strong>of</strong> this study was
evaluated the effectiveness <strong>of</strong> <strong>edible</strong> <strong>chitosan</strong>-<strong>linseed</strong> <strong>mucilage</strong> <strong>coating</strong>s to extend the shelf-life <strong>of</strong>
strawberries minimally processed.
MATERIALS & METHODS
Strawberries (Fragaria ananassa cv. Albion) were purchased from a producer-provider under the trademark
HamBerry® (Aguascalientes, México) and were inspected for no sign <strong>of</strong> physical damage, disease and visual
decay. Strawberries were sorted to select those with 2/3 <strong>of</strong> their red colour and being <strong>of</strong> uniform size.
Mucilaginous material was extracted from brown <strong>linseed</strong> (Linum usitatissimum) purchased from a local
wholesale distributor by mixing the seed with distilled water (1:20 w/v), stirring the seed-water mixture for 1
h at 40°C. The <strong>mucilage</strong> extract was separated from seed by filtration trough a mesh-using vacuum and to
obtain polymer the mucilaginous material was ethanol precipitate (1:1.5 v/v) and recovered by evaporation <strong>of</strong>
the solvent and drying.
Coating solutions FA, FB and FC were prepared by dissolving 1.5, 1.2 and 1.0% w/v <strong>of</strong> <strong>mucilage</strong> polymer in
aqueous dispersion, <strong>chitosan</strong> with a deacetylation degree <strong>of</strong> 75% (1% w/v) (Sigma-Aldrich N. C3646), lactic
acid 0.5% (Hycel) and Glycerol 0.6% (Fermot). The pH <strong>of</strong> the formulations <strong>of</strong> <strong>edible</strong> <strong>coating</strong>s were ~ 4.5-
5.2.
Strawberries were washed and sanitized by immersion into a 4 mL/10 l <strong>of</strong> Nicon-PQ® for 3 min. After
draining, the fresh-cut strawberries were dipped in the <strong>coating</strong>s solutions FA, FB and F2 for 8 min. Uncoated
strawberries were used as a blank and coated strawberries without <strong>chitosan</strong> in the formulation was control.
After the <strong>coating</strong>s process, samples were dried by natural convection for 2 h at 12 °C and were packed and
stored in polystyrene bags at 4 ° C.
Weight loss was expressed as the percentage loss <strong>of</strong> the initial total weight. For each measurement, 25 fruits
corresponding to each treatment were used and the experiment was performed in triplicate.
Respiration rate was determined by using the static method. Eight strawberries were placed in hermetically
sealed 875 ml glass jars and kept at 10 °C. After 1 h <strong>of</strong> enclosure, a 100 µl sample was withdrawn from the
headspace and analyzed for O 2 and CO 2 using a gas analyser (PBI Dansensor). Respiration rate (RR i , mg kg −1
h −1 ) <strong>of</strong> the samples in terms <strong>of</strong> CO 2 generation and O 2 consumption was determined from the slope <strong>of</strong> the
fitted linear equation, as described by [10].

Strawberry external colour was evaluated with a colorimeter (Minolta CR-400) CIE L*a*b* coordinates were
recorded using C illuminant and a 2° Standard Observer as a reference system. Three readings were taken at
different locations on each strawberry, during storage at 0, 5, 10, 15 and 20 days
Mechanical properties were measured by using a Texture Analyser (TA-XT-plus, Stable Micro Systems),
using a 75 mm diameter plate probe. Strawberry samples were 95% compressed at a 0.2 mm/s deformation
rate. Force and distance at the rupture point were used as mechanical parameters.
Decay rate (lost <strong>of</strong> visual quality, arbitrary scale) <strong>of</strong> strawberries that showed any sign <strong>of</strong> surface mycelia
development, dehydration, spots, colour changes, tissue damage, tissue collapse were considered decayed.
Results were expressed as percentage <strong>of</strong> damaged strawberries.
Microbial growth was determined <strong>of</strong> 10 g <strong>of</strong> strawberries was removed from each package and homogenized
with 90 mL sterile water in a sterile plastic bag, by use <strong>of</strong> a Seaward 400 Stomacher for 3 min. Decimal
dilutions were then prepared and plated onto appropriate media. The media and the incubation conditions
were as follows: mesophilic aerobic count (Plate count agar, Bioxon), incubated at 35±1 °C for 48 h for total
coliforms (Violet red bile agar, Bioxon) incubated at 37±1 °C for 24 h and for moulds and yeasts (Potato
dextrose agar, Bioxon) incubated at 25±1 ◦C for 72 h. All microbial counts were reported as log CFU/g
(colony forming units per gram <strong>of</strong> sample). The cell load data <strong>of</strong> each microbial group, collected during the
storage <strong>of</strong> the products, were modelled according to Gompertz equation modified by [11] during storage (0,
5, 10, 15, 20 days):
{ − exp[( µ e / A)(
λ − ) 1] }
y = k + Aexp max
t +
(1)
where y is the log[CFU/g], k is the initial level <strong>of</strong> the dependent variable to be modelled, A is the maximum
increase <strong>of</strong> bacterial load attained at the stationary phase, µ max is the maximal growth rate (∆log
[CFU/g]/day), λ is the lag time (days) and t is the time.
RESULTS & DISCUSSION
Weight loss was expressed as percentage loss <strong>of</strong> the initial total weight (Figure 1) all samples showed a
progressive loss <strong>of</strong> weight during storage, after the fifth day <strong>of</strong> storage weight losses for strawberries coated
with <strong>chitosan</strong>-<strong>linseed</strong> <strong>mucilage</strong> (FA, FB & FC) were significantly lower (p

metabolic pathways <strong>of</strong> coated strawberries. The addition <strong>of</strong> this type <strong>of</strong> <strong>coating</strong> is likely to modify the
internal atmosphere without causing anaerobic respiration, since <strong>chitosan</strong>-<strong>linseed</strong> <strong>mucilage</strong> <strong>edible</strong> are more
selectively permeable to O 2 than to CO 2 [9].
2.5
2
Respiratory quotient
1.5
1
0.5
0
Blank Control FA FB FC
Sample
Figure 3. Visual lost quality <strong>of</strong> coated, blank and control strawberries stored at 10 ◦C.
One <strong>of</strong> the best parameters to describe the variation <strong>of</strong> colour is the colour differences (∆E*), as it shows the
total change in all parameters L *, a * b *, (Figure 4) the changes during storage were visually perceptible to
an end. Uncoated fruits were darkens, skin colour becomes less chromatic and surface browning develops.
Firmness (Figure 5) significantly decreased during storage for all samples, these changes, which can be
attributed to tissue senescence and cell wall breakdown, as well as to the sample water loss, were
significantly less marked in coated strawberries.
14
2.0
12
∆E*
10
8
6
Firmness (N)
1.5
1.0
4
0.5
2
0
Blank Control FA FB FC
Sample
0.0
FA FB FC Blank Control
0 5 10 15 20
Storage time (days)
Figure 4. Colour difference <strong>of</strong> strawberries coated,
blank and control at end <strong>of</strong> storage time.
Figure 5. Firmness strawberries coated, blank
and control during storage time.
Under refrigeration, the antimicrobial activity <strong>of</strong> <strong>chitosan</strong> seemed to influence significantly the growth <strong>of</strong>
mesophilic bacteria. Edible <strong>coating</strong>s <strong>chitosan</strong>-based displayed a strong inhibition for all microbial groups; the
presence <strong>of</strong> <strong>chitosan</strong> on coated strawberries were significant difference between uncoated or control
strawberries (Table 1.).
Table 1. Gompertz parameters <strong>of</strong> mesophilic bacteria
Sample
Gompertz parameters a,c
A µ max λ R 2
Blank 6.9 3.0 0.45 0.995
Control 4.3 7.0 0.39 0.998
FA 1.7 2.5 0.18 0.995
FB 1.3 2.6 0.21 0.997
FC 1.5 3.0 0.15 0.989

CONCLUSION
The use <strong>of</strong> <strong>edible</strong> <strong>chitosan</strong>-<strong>linseed</strong> <strong>mucilage</strong> applied at strawberry fruits is recommended to control browning,
firmness lost, microbial growth and decay in strawberry fruit in combination with other methods, i.e. low
temperature and suitable packaging.
REFERENCES
[1] Khwaldia K. Perez C. Banon S. Desobry S. & Hardy J. 2004. Milk proteins for <strong>edible</strong> films and <strong>coating</strong>s. Critical
Review in Food Science and Nutrition, 44, 239−251.
[2] Xu W. T. Huang K. L. Guo F. Qu W. Yang J. J. Liang Z. H. 2007. Postharvest grapefruit seed extract and <strong>chitosan</strong>
treatments <strong>of</strong> table grapes to control Botrytis cinerea. Postharvest Biolology and Technology, 46, 86−94.
[3] Cha D. S. & Chinnan M. S. 2004. Biopolymer-based antimicrobial packaging: A review. Critical Review in Food
Science and Nutrition, 44, 223−237.
[4] McHugh T. H. & Krochta J. M. 1994. Milk-protein-based <strong>edible</strong> films and <strong>coating</strong>s. Food Technolology, 48,
97−103.
[5] Pierro P. D. Chico B. Villalonga R. Mariniello L. Damiao A. E. Masi P. 2006. Chitosan-Whey protein <strong>edible</strong> films
produced in the absence or presence <strong>of</strong> transglutaminase: Analysis <strong>of</strong> their mechanical and barrier properties.
Biomacromolecules, 7, 744−749.
[6] Tournas V. H. & Katsoudas E. 2005. Mould and yeast flora in fresh berries, grapes and citrus fruits. International
Journal <strong>of</strong> Food Microbiology, 105, 11−17.
[7] Hernández C., Pérez-Cabrera L. E. & González-Martínez C. 2010. Development <strong>of</strong> Linseed-Mucilage Edible
Coatings and its Application to Extend Fresh-cut Cucumber Shelf-life. In Regalado C. & García B. E. (Eds.).
Innovations in Food Science and Food Biotechnology in Developing Countries. Inc. AMECA, A. C. Queretaro,
Mexico. p 321-334.
[8] Mazza G. & Biliaderis C. G. 1989. Functional properties <strong>of</strong> flax <strong>mucilage</strong>. Journal <strong>of</strong> Food Science, 54, 1302-1305.
[9] El Ghaouth A. Ponnampalam R. Castaigne F. & Arul J. 1992. Chitosan <strong>coating</strong> to extend the storage life <strong>of</strong>
tomatoes. Horticultural Science, 27, 1016–1018.
[10] Fonseca S.C. Oliveira F.A.R. Jeffrey K. Brecha J.K. 2002. Modelling respiration rate <strong>of</strong> fresh fruits and vegetables
for modified atmosphere packages: a review. Journal <strong>of</strong> Food Engineering, 52, 99–119.
[11] Zwietering M.H. Jongenberge I. Rombouts F.M. van’tRiet K. 1990. Modelling <strong>of</strong> bacterial growth curve. Applied
and Environmental Microbiology, 56,1875–1881.