Impact of volatile allyl isothiocyanate on fresh produce

Highlights

• Gaseous allyl isothiocyanate was evaluated as natural preservative for packaged fresh produce.

• Gaseous allyl isothiocyanate exhibits antimicrobial activity on sprouts and iceberg salad.

• Even low amounts of allyl isothiocyanate negatively affect the quality of sprouts and iceberg salad.

Abstract

The applicability of allyl isothiocyanate (AITC) for the preservation of mung bean sprouts as well as fresh-cut iceberg lettuce was investigated. For this purpose, produce samples were stored in high gas barrier plastic bags containing a filter paper soaked with AITC (10 μl). Microbial loads as well as color changes and respiration of both products were monitored over 9 days of storage at 5 °C. The results showed that AITC (0.81–1.41 μg/ml) exhibits strong antimicrobial properties via the gas phase against the native microflora of iceberg lettuce and mung bean sprouts. However, the quality of both tested products was significantly affected, which limits the applicability of AITC for such sensitive produce commodities. The respiration activity of mung bean sprouts and fresh-cut salad was decreased by AITC while discolorations as well as changes to the texture were evident even at low concentrations (0.11–0.16 μg/ml), which did not provide antimicrobial effects.

Introduction

Within the last years, significant research has been focused on seeking new strategies to preserve fresh produce, especially industrially processed and packed fruits and vegetables (Meireles, Giaouris, & Simões, 2016). This commodity represents particularly perishable foods since cutting and peeling remove the protecting shell, increase cross contaminations and expose the tissue, which usually causes accelerated deterioration due to microbial growth, tissue softening or water loss. Especially sprouts are known to be very vulnerable to microbial spoilage since conditions during germination (high humidity and temperatures) usually lead to high microbial loads (Abadias, Usall, Anguera, Solsona, & Viñas, 2008; BfR, 2011). Allyl isothiocyanate (AITC) is a naturally occurring compound with a strong typical flavor, which is well-known from mustard, horseradish or wasabi. Isothiocyanates occur in plants belonging to the family of cruciferae where they derive from glucosinolates, a group of glucosides stored in the cell vacuoles (Delaquis & Mazza, 1995; Sekiyama, Mizukami, Takada, & Numata, 1994). Their antimicrobial activity has been known for long, which is why they have been used as biocides in agriculture and forestry or also as natural antimicrobials in food applications in Japan (Lin, Kim, Du, & Wei, 2000; Sekiyama et al., 1994). However, the broad application of AITC for food preservation is still limited although many studies have proven its efficiency to inactivate food pathogens or spoilage microorganisms (Dufour, Stahl, & Baysse, 2015), especially yeast and molds but also bacteria (Pires et al., 2009). AITC has been generally recognized as safe by the Food and Drug Administration (Delaquis & Mazza, 1995; Otoni, Soares, Silva, Medeiros, & Baffa Junior, 2014) and it has been shown not to be carcinogenic in mice (EFSA, 2010). AITC has been tested as volatile preservative for a bunch of different foods like cottage cheese (Gonçalves, Junqueira, Dos Santos Pires, Soares, & Araújo, 2009), mozzarella cheese (Pires et al., 2009), spinach leaves (Seo et al., 2012), peanuts (Otoni et al., 2014) or minimally processed shredded cabbage (Banerjee, Penna, & Variyar, 2015) with very promising results. However, reports about the impact of AITC on quality attributes of food are rare and the effect of AITC on very sensitive products like fresh cut salad or mung bean sprouts has not been elucidated so far. The purpose of this study was therefore to assess the suitability of volatile AITC regarding the inhibition or inactivation of naturally occurring microorganisms on fresh cut iceberg lettuce and mung bean sprouts as well as its impact on food quality.