Postharvest Physiological Disorders and Organoleptic Properties in Relation to Fungal Disease Incidence in Citrus

Hafiza Mehwish Iqbal1, Shahid Yousaf1, Salman Khurshid1*, Qurrat Ul Ain Akbar1, Saqib Arif1, Nasreen Fatima2 and Ali Murad Rahoo3

1Food Quality and Safety Research Institute, SARC, PARC, Karachi University Campus, Karachi, Pakistan; 2Department of Chemistry, Karachi University, Karachi, Pakistan; 3Wheat Research Center, Sukrand, Sindh, Pakistan.

Received | March 05, 2019; Accepted | June 25, 2019; Published | June 29, 2019

*Correspondence | Salman Khurshid, Food Quality and Safety Research Institute, SARC, PARC, Karachi University Campus, Karachi, Pakistan; Email: salmankhurshid67@gmail.com

Citation | Iqbal, H.M., Yousaf, S., Khurshid, S., Akbar, A.A., Arif, S., Fatima, N. and Rahoo, A.M., 2019. Postharvest physiological disorders and organoleptic properties in relation to fungal disease incidence in citrus. Journal of Innovative Sciences, 5(1): 6-11.

DOI | http://dx.doi.org/10.17582/journal.jis/2019/5.1.6.11

Keywords | Citrus, Physiological disorders, Organoleptic properties, Correlations

1. Introduction

Citrus fruit is popular as a source of vitamin C, flavonoids and phenolic compounm ds. It is a leading fruit being produced in the Pakistan and shares about 30% of total fruits production in the country. Most of the citrus is being consumed locally and about 10% of total production is exported to other countries. Substantial losses (20 to 50%) have been recorded due to improper post-harvest handling and practices (Olsen et al., 2000; Milind, 2008; Droby, 2006; Zhu, 2006). Mechanical damage likely to occur at the time of fruit handling (Sanches et al., 2008) and resulted into unfavorable changes in fruit quality, taste, nutritional value, color and shelf life (Durigan et al., 2005) and decrease in the vitamin C content (Lee and Kader, 2000). The deleterious cause of mechanical injury is decreased in acid content of fruits such as tomato, guava, mango and peach has been reported (Mattiuz and Durigan, 2001; Durigan et al., 2005; Kasat et al., 2007). Improper storage and transportation are also known to provoke growth of microorganisms due to changes in physiological condition of fruits and vegetables (Singh and Sharma, 2007).

Quality of citrus like other fresh fruits can be assessed through color, firmness, total soluble solids, total acid and sugar-acid ratio characters etc. Low pH, higher moisture content and nutrient composition of fruits induces pathogenic fungi, which make them less palatable (Moss, 2002; Olsen et al., 2000; Milind, 2008; Singh and Sharma, 2007). Infection can be easily transferred from single to groups of adjacent fruits. (Jay, 2003). Aspergillus spp. Produces mycotoxin that is unsafe for humans and animals’ life (Hejri et al, 2013). During packaging, Penicillium species enters into the tissue and deteriorates the fruit quality.

Annually, diseases from fungal pathogens causes severe losses to production of agricultural and horticultural crops every year (Parveen et al., 2016). Successful postharvest management is a potential solution which requires certain activities to be planned and performed at appropriate time. Initially, scientific based information is required on the incidence of diseases and their influence on fruit quality. This study has therefore been designed to identify the main fungal threats to the locally produced citrus and their quality indices being affected from pathogenic fungal attacks.

2. Materials and Methods

2.1 Collection of samples

The experiment was carried out to evaluate the incidence of postharvest physiological disorders, fungal contamination and changes in organoleptic characteristics of the citrus (citrus sinensis) quality. Thirty six samples of citrus fruit were collected from three different local markets namely new Sabzimandi (market 1), Saddar (market 2) and Liaquatabad (market 3) of Karachi. Considering physical appearance, sample representing each market contained six injured and six healthy fruits. The collected samples were transported to the lab in sterile polythene bag with proper packing and labelling.

2.2 Sample preparation

Samples were washed with 0.01% sodium hypochlorite (NaOCl) solution to avoid microbial contamination on surface and dried at room temperature.Samples were peeled off and seeds were separated from pulpy portion prior to blending.

2.3 Culture media preparation

Potato Dextrose Agar (PDA) is used as general culture media for isolation of fungi. A 39 g of commercial PDA powder was added to 1L of distilled water. Chloromphenicol (30mg/L) was added to prevent the bacterial growth. The mixture was dissolved under continuous stirring and boiling. Culture media was autoclaved for 15 min at 121oC.

2.4 Isolation of fruit spoilage fungi

Samples were cut into small pieces (2-3mm). The pieces were then transferred to sterilized and solidified media plates of potato dextrose agar (PDA). These plates were completely wrapped with parafilm and placed in incubator. The inoculated plates were incubated at 25-30oC for 5-7 days. The growth of fungal colonies was observed and recorded. The cultures were then subjected to purification according to the procedure described by (Parey et al., 2013).

2.5 Identification of isolated fungi

The fungal colonies were identified on the basis of macroscopic properties (colour, shape and appearance) and microscopic characteristics (like conidia shape, hyphae septations and other structures). The microscopic examination was undertaken under microscope at magnification of 10X and 40X (Tafinta et al., 2013; Samson and Varga, 2007).

2.6 Physiological quality analyses

Samples were examined for physiological parameters viz. total soluble solids, titratable acidity and pH. Digital refractometer (Hanna’s, HI 96801) was used for total soluble solids. Titratable acidity was determined through titration method. The pH values were measured with bench top pH meter (HANNA, HI 3512, USA). The sugar acidity ratio was also calculated by dividing the Total Soluble Solids values with acidity values (AOAC, 2010).

2.7 Organoleptic evaluations

Organoleptic evaluation of samples was carried out by a trained panel of 12 judges by following the method recommended by Larmond (1977). Each sample was presented to judges in random order. Judges evaluated the samples by assigning scores ranges from 1-9, where 1 and 9 represent extremely “dislike” and extremely “like”, respectively. On the basis of total organoleptic score, the samples were classified as “excellent” (score ≥ 8), “good” (score between 6-8), “fair” (score ≥5) and “poor” (score ≤ 5).

2.8 Statistical analysis

Samples were analyzed in triplicate for each parameter. Mean and standard deviations were determined. Correlation coefficients (r) were evaluated between the test parameters to assess the dependency of parameters on each other. The statistical analyses were performed by using SPSS software (SPSS version 17, Inc., USA).

3. Results and Discussion

This study conducted to evaluate specific fungal incidence and physico-chemical changes in injured and healthy fruits. Different quality parameters including pH, total soluble solid (TSS), percent acidity, sugar-acid ratio and organoleptic properties were evaluated in relation to pathogenic incidence.

 

Figure 1 shows the percent incidence of fungal pathogens in citrus. Results show that five different species of fungi viz. Aspergillus niger, Fusarium oxysporum, Rhizopus stolonifer, Aspergillus flavus and Alternaria alternata were identified. The most prevalent species were found to be Aspergillus niger with the incidence of 41.6%. Aspergillus spp. are one of the most common species found on different kinds of fruits like apple and grapefruits, oranges and mango (Abdullah et al., 2016). Long time transportation and high humidity supports the growth of Aspergillus spp. rot of fruits. Temperature plays an important role in the activities of fungi, high temperature enhances the spoilage of fruits (Fatima et al., 2012). In the present study, the second most prevalent species was Fusarium oxysporum (27.7%). Whilst, the lowest incidence was observed for Rhizopus stolonifer (8.3%).

Figure 2 presents the detailed number of infected samples found in three selected markets. Three species viz. Rhizopus stolonifer, Aspergillus flavus and Alternaria alternata were rarely identified in one fruit market. The Aspergillus spp. is underlying mediator of post-harvest deterioration of fresh fruits in Pakistan. Sugary flavor and low pH level of acidic fruits favors the attack by Rhizopus spp. (Al-Hindi et al., 2011; Gadgile and Chavan, 2010; Diedhiou et al., 2007; Muhammad et al., 2011).

 

Figure 3 shows the physiological disorders of infected citrus and their comparison with the healthy citrus. A remarkable difference can be seen between infected and healthy citrus in terms of their pH, TSS, acidity and sugar to acid ratio. Total soluble solids of infected citrus (8.8%) were significantly lower than the healthy citrus (13.6%). Reduction of total soluble solids in injured fruits can be related to the use of these compounds as respiratory substrate since there is an increase in CO2 production in relation to intact fruit (Mattiuz and Durigan, 2001). Also, sugary flavor in the citrus fruits attracts the pathogens for their growth and contamination. Higher temperature increases the metabolism rate and hydrolysis of starch that finally decreases the TSS (Thompson, 1996).

 

Titratable acidity is a key attribute of fruits quality that reveals either condition is favorable or adverse for fungal growth. In this study, it was found to be higher in healthy citrus as compared to infected samples (Figure 3). Besides increasing level of maturity, the infection and injury also leads to the reduction in acidity of fruit (Abbasi et al., 2009; Padayatty et al., 2003; Rickman et al., 2007). Alternately, the pH values were found lower in infected samples as compared to healthy samples. The differences were statistically significant (p<0.05).

Compositional changes also affected the organoleptic quality of fruit leading towards the change in acid and sugar ratio that directly influence the taste of fruit. We have also found strong relationships (r = 0.84 to 0.99) between physiological and sensory attributes of citrus (Table 1). Iincidence of fungal infection is an indication of fruit injury by physical or mechanical and over ripening of fruits that alter the physiological condition of fruit and ultimately change the sensory attributes of fruit.

 

Table 1: Relationship between physiological and organoleptic properties of healthy and infected citrus.

Quality parameters	Color	Texture	Taste	Overall acceptability
pH	-0.87	-0.94	-0.95	-0.95
TSS	0.87	0.95	0.99	0.96
Acidity	0.86	0.85	0.91	0.93
Sugar-acid ratio	-0.85	-0.84	-0.91	-0.93

 

Table 2: Sensory evaluations of infected and healthy citrus fruits.

Sample type		Sensory attributes
		Color	Texture	Taste	Overall Acceptability
Infected fruit	1	5	5	5	5
	2	5	4	5	5
	3	5	4	5	4
	Mean	5 a	4 a	5 a	5 a
Healthy fruit	1	7	8	7	8
	2	8	7	8	8
	3	8	9	8	8
	Mean	8 b	8 b	8 b	8 b

Sensory scoring: ≥ 8: excellent score, 6-8: good score, ≥5: fair score and ≤ 5: poor score; Mean value with different letters represents statistically significant (p<0.05) difference.

 

Results of sensory evaluation of infected and healthy citrus samples are given in Table 2. All the sensory attributes including colour, texture, taste and overall acceptability were significantly influenced (p<0.05) by fungal infection. Fungal infection changes the colour of fruit, brown to black infected lesions produced by Alternaria spp. Further, such fungal spoilage changes the aroma, taste and texture of fruit and become undesirable for human use (Gorny and kader, 1996). Cold weather dried the fruit pulp and brownish spots are appear on the outer surface of fruits. Yellow to brown leathery areas developed due to sunburn. Pesticide or herbicide injury causes necrotic spots on fruits that resemble with rot (Begeman and Wright, 2009). Improper cultural practice and Over nitrogen dose can produce thick peel of orange that influence on quality (Corinne Rhodes, 2014). Cracks produce on skin during handling and harvesting allows the fungus entry therefore, rough handling produce sunken spots on upper layer of fruit (Hui and valley, 2008).

 

Author’s Contribution

All author of the manuscript contributed equally in overall planning, sample analysis, data interpretation and writing of research article.

 

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